Immune Response Ebook

How To Bolster Your Immune System

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Immunity Crisis

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Immune System Suppression

Dioxins have been shown to alter the immune system in a wide variety of animals. For example, dietary exposure to PCDDs and PCDFs and coplanar PCBs has been correlated with immunosuppression in field experiments with harbor seals. Dioxin and PCB-mediated immunosuppres-sion is believed to have contributed to the mass mortalities of seals and dolphins in European waters in the late 1980s and early 1990s. PCDDs Fs are known to cause hypertrophy of the thymus, which is the site of production of mature T-lymphocytes, which are indispensable for the development and maintenance of the T-cell-mediated portion of the immune system. Because dioxins affect maturation and specialization of T-cells, exposure is believed to reduce the organisms' ability to fight off harmful bacteria, viruses, and other substances.

Melanization a conserved immune response based on speciesspecific regulatory modules

It would appear therefore, that the specificity of the otherwise ubiquitous process of melanization derives from its tight regulation by genetic modules that probably co-evolve with pathogens. The modular mix-and-match evolution hinders detailed knowledge transfer between species, but elegantly illustrates the flexibility of the immune system to correctly identify specific threats and then activate a potent immune response.

The immune response varies with the time of day

The immune response and circadian clock regulate each other, potentially causing feedback loops that are predicted to cause a physiological collapse in some situations but in others might increase an insect's defences. Flies exhibit a circadian rhythm in which they are active during the day and less active at night. The molecular pacemaker that controls these rhythms is defined by the genes period, timeless, clock, and cycle (per, tim, clk, and cyc) (Nitabach and Taghert, 2008). The genes per and tim are transcribed and the Tim and Per proteins together form a negative transcriptional regulators of the clock and cycle genes. The Clock and Cycle proteins are positive transcriptional activators of the per and tim genes. Thus as Per and Tim levels rise, this represses the production of Clock and Cycle which ultimately causes Per and Tim levels to fall. Mutants in per or tim show an activity pattern where active and inactive periods are dispersed throughout the day rather than being...

Conclusion inherited symbionts and the evolution of host immune systems

The previous two sections argue first that sym-bionts can actively contribute to resistance to natural enemies, and second that many of them will also interact with the immune system of the host. What are the consequences of these for immune system The second issue raised in this chapter was the interaction between symbionts and the immune system of the host. The observation that symbionts can interact with host immune systems indicates we should ask whether symbionts have produced selection for immune systems that accommodate them It is notable that the insect immune system, despite being classically considered 'generalist' in its action, still shows some evidence of being fast-evolving, both in terms of the strength of positive selection and the turnover of elements within the systems. The signature of positive selection is particularly strong in the signalling components of the humoral immune cascade (Begun and Whitley, 2000 Jiggins and Kim, 2007), although interestingly not in the...

The effects of physiological state on immune function can mask mimic or mediate tradeoffs

Selection should lead to the allocation of these resources in such a way as to maximize fitness. Following this logic, it has been suggested that insects, like other animals, increase the energy available for reproduction by depressing immune function (see Siva-Jothy et al., 2005 Lawniczak et al, 2007). Therefore insect ecological immunologists have searched for trade-offs between reproduction and immune function (Siva-Jothy et al, 2005). Trade-offs occur when two traits are functionally connected, such that an increase in one trait leads to a reduction in the other (Zera and Harshman, 2001). Unfortunately, two traits can be negatively correlated even when there is no functional connection between them (Zera and Harshman, 2001). Without knowing the physiological mechanisms connecting two traits, it is impossible to know whether they are functionally linked (Harshman and Zera, 2007). This observation is especially true for trade-offs involving the immune...

Assessing immune function across different physiological states

As discussed above (sections 11.2.1.4 and 11.3), researchers should be sensitive to the underlying physiology of the immune system and interconnected physiological systems when they design and interpret immune assays. Knowledge of the physiological details will help experimenters to determine the suite of immune measures they need to test their hypotheses. Single measures of immune function are known to give a poor overview of immune system health (Luster et al., 1993 Keil et al., 2001). For example, sexually active male Drosophila melanogaster remove non-pathogenic bacteria from their bodies more slowly than do males that lack mating opportunities (McKean and Nunney, 2001). McKean and Nunney (2001) concluded from these results that there is a negative trade-off between male sexual behaviour and disease resistance. However, Corby-Harris et al. (2007) found that the ability to clear bacteria from the haemolymph does not correlate with the ability to survive a bacterial challenge in D....

Interpretation of assays of immune function

The correct interpretation of measurements of immune function (e.g. PO activity, haemocyte count, etc.) remains a problem for ecological immunologists (Adamo, 2004a Martin et al., 2006). One complexity rarely noted is that an animal's physiological state can alter the relationship between an immune measure and disease resistance. For example, immediately after acute stress, an increase in some immune assays can correlate with a decrease in resistance to pathogens (Adamo, 2008b). Similarly, D. melanogaster females increase expression of immune-related genes after mating (Domanitskaya et al., 2007 Fedorka et al, 2007), but show a transient decrease in resistance to bacterial infection (Fedorka et al., 2007). The contradictory results found among studies on trade-offs between reproduction and immune function may be partly due to uncontrolled variations in the physiological state of the subjects (Harshman and Zera, 2007). Another difficulty in measuring immune function arises because...

Evolutionary patterns in the antimicrobial immune response

Is shown by elevated rates of amino acid substitution between species and by elevated rates of duplication within gene families. The availability of whole-genome sequences allows for quantitative contrasts to be made between immune and non-immune genes, as well as for comparisons between functional classes of immune response genes. The recent complete genome sequencing of 12 species of fruit flies in the genus Drosophila has allowed particularly fine measurement of rates of substitution and genomic rearrangements between Comparative genomic and molecular evolutionary analyses have revealed that not all genes in the immune system evolve along the same trajectories. Genes in broadly defined functional categories differ in evolutionary mode, suggesting contrasting selective pressures based on gene function. The supporting data and potential selective pressures that drive these evolutionary patterns will be considered in detail.

Epithelial immunity the local immune response

The systemic immune response has been studied through the direct introduction of pathogens into the body cavity. This approach has limited the study of the immune response to the steps involved in recognition and antimicrobial response in the fat body. While these studies have revealed insights on the molecular basis of the Drosophila immune response, they may not reflect the most common mode of host interaction with potential pathogens. In metazoans, the epithelia of the digestive, respiratory, and genital tracts are constantly exposed to microbes of both indigenous and environmental origin. Thus, these routes have the potential to be the major routes of infection for a host. The next section of this chapter will focus on the immune epithelial response. 2.3.1 A gut-associated immune system The systemic mode of infection bypasses the layered steps of a given host-microbe interaction by directly activating the immune response. The mere presence of a microbial elicitor is sufficient to...

Evolutionary patterns in the antiviral immune response

Early characterization of the immune response focused primarily on antimicrobial defence. Antiviral defence is at least partially distinct from that against microbes, and currently is only poorly understood. Both the Toll and Imd pathways are activated during the course of some viral infections however, only the Toll pathway seems to confer protection (Lemaitre and Hoffmann, 2007). RNAi provides an independent mechanism of defence that is specific against RNA viruses (Wang et al., 2006). Viruses are formidable opponents for the immune system. They are capable of rapid evolution owing to their fast generation times, large population sizes, high mutation rates and obligate pathogen lifestyles. These factors hint that the evolutionary patterns of antiviral defence genes will be different from those described previously for the antimicrobial defence.

Host Defences and Parasitoid Counterstrategies

The most significant challenge confronting parasitoid larvae is survival in the host. The first line of defence available to hosts is to avoid being parasitized at all by either hiding or fending off oviposition by the parasitoid adult. Once oviposition occurs, however, the host's immune system serves as the main defence against the parasitoid egg and larva. Insect blood contains cells called haemocytes, which have many different functions in immunity. The main immune response to large, multi-cellular invaders, such as parasitoids, is encapsulation. Although some Diptera form melanotic capsules without the apparent participation of haemocytes (Carton and Nappi, 1997), haemocytes are responsible for encapsulation in most other insects (Strand and Pech, 1995). The insect immune system does not recognize specific entities, but it is able to recognize classes of foreign objects, using pattern-recognition receptors (PRRs) (Medzhitov and Janeway, 1997). For example, certain PRRs recognize...

Why Sexual Reproduction in Parasites

Interactions, which results in differential fitness for both hosts and parasites (for a review, see Ladle, 1992). Sex will increase the evolutionary rate of hosts, whose reproductive (and hence evolutionary) rate is generally slower than that of their parasites (Jaenike, 1978 Hamilton, 1980). Therefore, sex accelerates the evolution of the host population, thus generating an ever-changing environment (e.g. the host immune system) for the parasite population (Seger and Hamilton, 1988 Hamilton et al., 1990). In response, parasites are expected to adapt to this changing environment, resulting in a coevolutionary arms race between the parasite and the host (Hamilton, 1993). Despite the higher intrinsic evolutionary rate of the parasite, intrinsic to its rapid life cycle, sex in parasites will provide an additional increase, enabling the parasite population to track the host population. As will become clear, the parasite's intrinsic evolutionary rate advantage does appear to enable more...

LMC and Sex Determination

Positively correlated with the gametocyte density, which the authors interpreted in terms of facultative LMC and which relies on one major assumption that gametocyte densities increase with the number of coinfecting clones. When there are multiple clones present, the parasite clones are expected to adjust their sex ratio in response to local conditions single clone infections produce low gametocytaemia and LMC predicts the maintenance of a female bias multiple clone infections result in a higher gametocytaemia and there is a facultative switch to a more equal sex ratio. This requires that coinfecting clones are able to estimate the number of coinfecting clones, which they could do using any number of cues, as long as the cues vary in intensity according to the number of clones present. In mouse malaria, coinfection resulted in significantly increased anaemia independent of parasitaemia in mixed rather than single infections, with an accompanying increase in gametocytaemia and...

Manipulation as a Functional Adaptation

For instance, let us assume that the energy invested into manipulation by a parasite is variable within a population and under genetic control. This is most probably true of most cases. We might expect that the more a parasite invests into manipulation of its intermediate host, the more it increases its probability of transmission to the definitive host beyond what it was initially. Without manipulation, the parasite might still be transmitted, but with a lower probability, P, corresponding to passive transmission. Manipulation enhances this probability, but with diminishing returns, i.e. small investments in manipulation yield greater returns per unit investment than larger investments (Fig. 12.2). Beyond a certain level of investment into manipulation, the probability of transmission approaches 1. At the same time, the costs of manipulation are also likely to increase in proportion to the investment in manipulation. Little is known about how costly it is for parasites to control the...

Selection and Virulence from the Hosts Perspective

For the host, virulence is any consequence of infection that reduces the host's lifetime reproductive success (fitness). A fitness cost could result from the direct damage done by the parasite (destruction of cells, usurpation of resources), the expenditure of resources in mounting an immune response and collateral damage done to the host by its own immune system. To better grasp how parasites can reduce reproductive success, we can partition fitness into components, such as lifespan, fecundity, number of reproductive episodes, ability to find and court mates and health of offspring. Trade-offs between these components of fitness are a universal challenge faced by organisms (Bell, 1997), so we can imagine that infection may hinder one component of fitness while benefiting another. For example, castration of the host may be beneficial to the parasite if infected hosts partition more resources towards growth and body maintenance, which could provide more resources for the parasite and a...

Selection and Virulence from the Parasites Perspective

Have been proposed - see below), and even more rarely is it actually tested (Mackinnon and Read, 1999a). The assumption that higher parasite loads lead to reduction in the host survival is supported by data on some pathogens (examples include HIV (Mellors et al., 1996) and rodent malaria (Mackinnon and Read, 1999a)), but the literature is replete with exceptions (Messenger et al., 1999). The actual relationship between parasitaemia and pathology may be non-linear, especially if the host's immune system is responsible for some part of the injury 'caused' by the parasite. In such cases, low parasite loads may be as harmful as moderate or even fairly heavy loads. For example, the destruction of liver and other organs seen in human schistosomiasis is in part a result of the host's immune attack on the microscopic eggs of the worm (Warren, 1975) and the anaemia presenting with malaria derives in large part from destruction of uninfected red blood cells by an overactive immune system...

Clonaldiversity hypothesis

For parasites that replicate within the host (malaria parasites and viruses are examples), the presence of multiple genotypes, or clones, may lead to competition for resources or simply to be the clone most likely to be transmitted. When infections typically consist of many clones, this would select for high parasite replication and higher virulence (van Baalen and Sabelis, 1995 Frank, 1996). Even if each clone is prudent and replicates slowly, the sum of the clone densities would result in higher virulence. High clonal diversity may also lead to some proto-cooperation by the parasites to elude the host immune system more efficiently, thus resulting in a higher rate of parasite replication and higher virulence.

Other consequences of infection for lizard hosts

Blood haemoglobin levels do not drop for infections of P. azurophilum, as might be expected, because this parasite infects only white blood cells. However, white blood cells infected with P. azurophilum produce less acid phosphatase, an important enzyme in the functioning of these immune-system cells (Schall, 1992). This suggests that anoles infected with P. azurophilum may have reduced resistance to infection with other parasites if their immune system is compromised. Unfortunately, no data on this issue are available (indeed, no data on the impact of malaria infection on resistance to other parasites exist for any lizard host).

Parasite Behaviours within the Host

In almost all cases, the host is treated as a black box, and parasite behaviours are usually defined and interpreted only within an ultimate context. However, the lack of proximate details illustrates the challenges to understanding the behaviour of parasites in their hosts. The major obstacles relate to the technical difficulty of observing parasites in situ. Almost all of our understanding of parasite proximate behaviours comes from observations made after the host has been opened and the parasites removed. These actions create dramatic changes in the parasites' environment, which render classical behavioural studies virtually impossible. Additionally, parasite responses may be state-dependent, and their proximate strategies will change with changing conditions in the host. For example, tapeworms alter their reproductive strategies in response to food deprivation in the host (Sukhdeo and Bansemir, 1996), and blood flukes reduce their blood feeding and egg production when in hosts...

Adults

If an appropriate vertebrate consumes a second intermediate host infected with one to several thousand metacercariae, the digestive process releases immature worms from the cysts. Excysted worms then migrate through the host to a specific site, which varies widely among species, but is often in the intestinal tract. To find an appropriate site within the host, helminths must respond to a number of cues in the host environment (Sukhdeo and Bansemir, 1996). Most ingested metacercariae do not become established, probably due to several levels of host defence, starting with mastication and including both general and specific immune responses. If the host is uninfected, the establishment of new infections can increase along with the number of metacercariae given in laboratory exposures, presumably because large numbers can catch the relaxed immune system off guard (Christensen et al., 1988). Some schistosomes may present trematode-derived antigens that mimic host antigens (Damian, 1967) or...

How insect immunity works

Broderick et al. (Chapter 2) first provide an overview of the best-understood insect immune system, that of D. melanogaster. They introduce the reader to one of the most important outputs of the fly's immune system the powerful array of antimicrobial peptides and proteins (AMPs) that provide a broad-spectrum systemic defence against not only prokaryotic microbes, but also eukaryotic pathogens and parasites, such as fungi and protozoa. They then review the twin transcriptional control regulatory systems, named after crucial components of the signalling pathways Toll and Imd, which govern the production of AMPs. They also take into consideration the as yet rather incompletely understood Janus kinase signal transduction and activators of transcription (JAK STAT) cellular control system that links Toll- and Imd-regulated responses with others (e.g. the complement-like TEP proteins and a whole host of cellular defences). In the second part of their chapter, the authors turn to the much...

Insect immunity and organismlevel interactions

Many insects harbour bacterial symbionts, often in their guts. As Hurst and Darby review in Chapter 8, evidence is accumulating to suggest that bacterial symbionts provide protection against other natural enemies, including fungi, viruses, parasitoids, and even predators. If they provide resistance, how does the evolutionary ecology of symbiont-mediated protection differ from resistance through the host's own immune system Although this is hardly studied, Hurst and Darby speculate that these symbi-onts are similar to constitutive defences the insect always pays a metabolic cost. However, secondary symbionts can be lost easily if the selection pressure exerted by a parasitoid relaxes, for example. Aside from protection, there is another twist to the story. In most cases, these symbionts will be expressing pathogen-associated molecular patterns (PAMPs) similar to, or the same as, those of the pathogen. Moreover, the host needs to ensure that the symbionts co-operate. This establishes a...

Permanent versus Inducible Defenses

Defenses can be permanent (constitutive) or inducible. Phenotypic plasticity in defensive traits enables prey organisms to express a particular defense only if a reliable cue for a future attack is present. Thereby, the organisms can minimize costs affiliated with the formation or maintenance of a defense when predation risk is low. Inducible defenses are an appropriate mechanism to cope with the variable hazard of a frequently changing predator spectrum. In the animal kingdom, inducible defenses cover a taxonomic range from protozoans to vertebrates. The defensive traits range from behavior, morphology, and life-history adaptations to the activation of the specific immune system of vertebrates. Daphnia show the most prominent examples of morphological plasticity triggered by chemical cues, so-called kairo-mones, released by predatory invertebrates and fish. For example, elongated helmets, tail spines, or crests have been shown to reduce predator-caused mortality (Figure 2).

Conclusions and future prospects

Although there has been significant progress in identifying and characterizing functions of plasma proteins that take part in innate immune responses of M. sexta, significant gaps remain in our knowledge, and important questions require further experimentation. There is a need to re-examine the mixture of antimicrobial peptides in plasma using modern purification and proteomics methods. It is likely that undiscovered peptides and proteins exist, with potentially useful and interesting functions. In this regard, little is known about antifungal gene products from Manduca, and future bioassays should include searches for such activities. Genediscovery efforts will require sequencing of the M. sexta genome at some point, to permit a thorough examination, and this will certainly yield a wealth of prospective immune system genes to be investigated experimentally. Future research may yield answers to intriguing questions about the functions of clip domains in protease cascades, as well as...

The emergence of Hivaids

This newly recognized immune-suppressing disease was initially referred to as Gay-Related Immune Deficiency (GRID). By mid-1982, however, GRID had also been diagnosed in IDUs, hemophiliacs, and individuals from Haiti, and was renamed AIDS. That AIDS was an epidemic was clear by the end of 1982. By 15 September 1982, the Centers for Disease Control (CDC) had received reports of a total of 593 cases of AIDS and noted that the incidence of AIDS by date of diagnosis had essentially doubled every six months since the second half of 1979 (CDC, 1982b). In San Francisco, the number of AIDS cases diagnosed in the second half of 1982 equaled the number of cases that had been diagnosed since the epidemic was first recognized (Moss et al., 1983). While the rate at which cases of AIDS were emerging was causing alarm among public health officials and gay activists, governmental and public response to the epidemic was minimal, especially when compared with other recent public health scares including...

Injection drug use and disease spread

Injection as a route of drug administration provides some obvious advantages to medicine doses can be measured precisely the absorptive limitations of the skin, gut, or respiratory mucosa can be bypassed and agents can be introduced directly into the bloodstream (in intravenous injection) for rapid distribution to target tissues. Indeed, keeping veins open (KVO) lines are used for precisely this reason - to allow rapid access to the circulatory system. But these tremendous advantages can be misused and can lead to grave complications. As the epidermal barrier of the immune system is effectively bypassed, unclean needles and syringes can result in direct inoculation of pathogens into the system. As such, risk of bacterial endocarditis in drug users, along with acquisition and transmission of classic blood-borne pathogens, including HIV, HCV HBV malaria, tetanus, and syphilis, is exacerbated in IDU. Further, the direct introduction of agents into the bloodstream means rapid intake and...

The immunoglobulin domain PRR family

The immunoglobulin domain plays a primary role in pattern recognition in the mammalian immune system. As a building block of antibodies, major histocompatibility complexes (MHCs), and other proteins that are responsible for making direct contact with pathogens, the immunoglobulin domain is evolutionarily engineered for the specific recognition and binding that is required for pattern recognition. Different subcategories of immuno-globulin domain may be recognized on the basis of sequence similarity, but the structure of the various domains tends to remain conserved within the superfamily. Immunoglobulin domains are characterized by a region of approximately 100 amino According to the broadest definition, the IgSF of any species contains genes encoding at least one immunoglobulin domain, as defined by a typical conserved sequence and structure. Although most thoroughly studied in mammals, immunoglobu-lin-domain-containing proteins in a wide range of species are responsible for...

Musth as advertisement of male quality to females

Females choosing males in musth for mating thus seem to be choosing males of high quality. This can be demonstrated even more convincingly when the cost imposed by musth on the functioning of their immune systems is considered but this is a subject that merits a separate discussion.

Cardiovascular System

Blood makes up about 7 of human body weight. In females this averages about 4.5 L of blood males about 5.5 L. When a tube of blood is centrifuged, the upper 55 of the volume will be a pale yellow liquid called plasma. Plasma is 90 water, with 10 solutes including proteins and electrolytes nutrients such as glucose, amino acids, and lipids and waste products such as urea and bilirubin, a waste product that gives plasma, as well as urine and feces, their color. About 96 of the plasma proteins consist of albumins and globulins. These have overlapping functions, including control of osmolarity and the transport of insoluble lipids, vitamins, metals, hormones, and so on. Globulins are an important component of the immune system, discussed in Section 9.7. The rest of the protein is fibrinogen, involved in blood clotting. The dominant electrolytes are sodium and chloride. Intercellular fluid is similar in composition to plasma. Just 0.1 of the blood volume is composed of white blood cells,...

Immunity And The Lymphatic System

The immune system consists of defenses against foreign matter that gains entry to the body. It consists of the lymphatic system plus components of numerous other systems of the body. Many toxic pollutants either stimulate or suppress the immune system. The lymphatic system consists of lymph, lymphatic vessels, lymphocytes, and lymphoid tissues and organs. Lymph is a fluid similar to plasma. Lymphatic vessels are similar in structure to veins. They conduct lymph from peripheral tissues to the veins. Capillaries deliver more liquid to tissues than they carry away. The rest forms intercellular fluid that collects as lymph. The most important lymphoid organs are the lymph nodes, the spleen, and the thymus. The lymph nodes contain immune system cells that remove pathogens from the lymph before they reach the bloodstream. The tonsils are lymph nodes positioned to respond to infections arriving by way of the mouth or nose. The thymus produces T cells (described below). The spleen performs...

Cytochrome P450Mediated Effects

Immune system suppression Dioxins are widely held to have effects on the immune systems of exposed animals. It is suspected that this type of effect contributed to the mass mortalities of seals and dolphins in European waters in the late 1980s and early 1990s. The mechanism for immune system effects is not well understood

Musth as a handicap Immune suppression by testosterone

As discussed, musth is an expensive proposition for male elephants in terms of the physiological costs involved. By the end of the musth period, the bull is in poor body condition. To that extent, a bull is handicapped by going through musth. There is, however, a much more serious handicap that a bull suffers when it is in musth, an aspect that has been overlooked by elephant biologists. The high levels of the major androgen, testosterone, associated with musth (or the development of secondary sexual characters, for that matter) also seriously impair the functioning of the immune system, exposing the male to debilitating parasitism and disease. While Hamilton and Zuk recognized their hypothesis to be a variation of the handicap principle, Ivan Folstad and Andrew Karter went a step further in more formally linking the parasite-male handicap idea with the immunocom-petence burden. The differences between males and females in hormone profiles need not be elaborated here. These hormonal...

Concepts and methods in comparative genomics

The volume of data from genome sequencing presents a wealth of opportunities, but also immense challenges to identify meaningful encoded elements, elucidate their functions, and interpret broad principles of genome evolution. Comparative methodologies have been instrumental for understanding important generators of diversity such as alternative splicing, and the extent and importance of non-protein-coding elements. It is now understood that recognizable biological functions are encoded by the interaction of a variety of elements protein-coding genes, non-protein-coding RNA genes, and conserved non-coding functional elements. The insights gained from comparative genomics, in combination with functional data, can propel comparative analysis stepwise, to the systems level from macromolecu-lar complexes to regulatory networks, signalling pathways, and coordinated physiological reactions to environmental stimuli, such as responses and modulation of the immune system. To this end,...

Drosophila establishing the framework of insect immunity

Immunity, although recognition of the capacity of insects to respond to invaders was initiated with the discovery of the antimicrobial peptide (AMP) cecropin in the giant cecropia moth (Steiner et al., 1981). The microbicidal properties of the haemo-lymph and the identification of numerous inducible AMPs therein, pointed to an insect immune system able to recognize and respond to invading pathogens. Regulatory DNA sequence motifs, resembling those recognized by mammalian nuclear factor kB (NF-kB), were detected in AMP gene promoters, providing the first parallel with mammalian innate immunity (Sun et al, 1991). These discoveries set the course for applying the power of Drosophila genetics to the elucidation of upstream components of two key immune-signalling pathways, Toll and Imd (immune deficiency). Together these pathways permit differential recognition and response to invading micro-organisms through signal transduction, leading to nuclear translocation of specific NF-kBs and...

Complexity as a Systems Concept

In coming to terms with complexity as a systems concept, we first have to realize that complexity is an inherently subjective concept what is complex depends upon how you look. When we speak of something being complex, what we are really doing is making use of everyday language to express a feeling or impression that we dignify with the label 'complex'. But the meaning of something depends not only on the language in which it is expressed (i.e., the code), the medium of transmission, and the message, but also on the context. In short, meaning is bound up with the whole process of communication and does not reside in just one or another aspect of it. As a result, the complexity of a political structure, an ecosystem, or an immune system cannot be regarded as simply a property of that system taken in isolation. Rather, whatever complexity such systems have is a joint property of the system and its interaction with another system, most often an observer and or controller.

Anopheles appreciating the diversity of insect immunity

Table 6.1 The established framework of insect innate immunity allows for the classification of genes and gene families into broad functional categories of recognition, modulation, signal transduction, and effector components as well as responses to oxidative stress and RNA. These categories consist of genes from pathways and protein families implicated in immune responses through experimental research, and together they form the basis of the currently recognized insect immune repertoire. Table 6.1 The established framework of insect innate immunity allows for the classification of genes and gene families into broad functional categories of recognition, modulation, signal transduction, and effector components as well as responses to oxidative stress and RNA. These categories consist of genes from pathways and protein families implicated in immune responses through experimental research, and together they form the basis of the currently recognized insect immune repertoire. Haematophagy...

Multispecies comparisons exploring the evolution of insect immunity

The availability of multiple sequenced insect genomes has greatly facilitated the dissection of their immune repertoires into functional modules and sequential phases of an integrated innate immune system response. Concomitant analysis of orthology, sequence variation, and functional data from experimentation has provided important insights towards understanding the principles that govern the ongoing evolution of innate immunity. The emergent picture is one of a robust architecture, shared to some extent even with vertebrates, but with diversified inputs and outputs. The observations that different immune modules have distinct and even contrasting evolutionary dynamics have helped explain the overall flexibility of a system capable of adapting to a multitude of new challenges.

Honey bee appreciating defence strategies other than immunity

The honey bee genome allowed the comparative analysis of an insect separated from Diptera by over 300 million years of evolution. Compared to the Dipteran genomes, the honey bee appears to have evolved slowly the mean sequence identity of its single-copy orthologues with human genes is higher than that between fruit fly and human, or mosquito and human. Moreover, the honey bee retains more ancient introns, and its gene losses and gains appear to be lower than in Diptera (HGSC, 2006). The honey bee genome has allowed a unique comparison of the immune repertoires between social and solitary insects. Behavioural studies of honey bees and other social insects have highlighted strategies that may have evolved to protect them against disease grooming and nest hygiene habits, prompt removal of infected larvae, and use of antimicrobial compounds in nest-building materials, result in a relatively sterile nest environment and a consequent dramatic reduction in exposure to pathogens. Indeed, the...

Th1Th2 Regulation Allergy and Hyposensitization

A widespread and successful therapy of allergy, hyposensitization, e.g., against bee venom, pollen, or house dust mites, consists in the initial phase in subcutaneous injections of increasing doses of allergen in varying intervals following empirical protocols. In the maintenance phase high doses of antigen are injected every 4 weeks for a period of several years 3 . During a venom immunotherapy a shift from a Th2-dominated

Insect immune defence mechanisms

I refer the reader to detailed descriptions of the individual components of insect immune systems provided in other chapters of this volume and just summarize them here. I count seven layers to the immune response, moving from the outside of an insect to the inside. First, is the native microbiota, which occupies niches on the surfaces of insects (both on the outside of the body and within the gut, for example) and can prevent colonization by other microbes. Second is the barrier epithelial immune response, which is induced to produce antimicrobial peptides (AMPs) when it recognizes a pathological event. Third is the clotting response, which can entrap microbes in a fibrous net. Fourth is the haemocyte-driven immune response, which can lead to phagocytosis, encapsulation, or nodu-lation of invading parasites. Fifth is the melaniza-tion response, which can produce reactive oxygen that presumably kills microbes. Sixth is the AMP response, in which the fat body releases large quantities...

Energy management and immunity

Energy flow in an organism is strictly regulated. One of the most common arguments in ecology seems to be that physiological programming decisions evolve in part based on the internal competition for resources. Many experiments imply that immune activation utilizes energy and takes that energy from other physiological activities but such changes can be difficult to assess directly because of compensatory changes in these other systems. Moret and Schmid-Hempel (2000) have provided a particularly clean example of this resource-allocation issue because the design deliberately limited the effects of compensation by starving the bumble bees that were the subject of the experiments. Unfed bumble bees die at a reproducible rate and obviously cannot compensate for energy use by eating more. If these bees are forced to raise an immune response then they die faster than un-manipulated bees, suggesting that the immune response is using energy that would otherwise be used to keep the bees alive....

The Idiotypic Network

The immune system defends the body against threats to its health caused by antigens, e.g., pathogenic cells or substances. A key feature of the immune response is the recognition of foreign invaders. In the humoral immunity, which is considered here, this is achieved by antibodies. Antibodies are proteins with highly specific binding sites, which enable them to bind to complementary sites of an antigen, which are thus marked for further processing, e.g., for eating by macrophages.

Predicting Future Extinction and Factors That Make Species Endangered

Tends to increase homozygosity because two related individuals are more likely to share the same version of a gene than are two unrelated individuals. Offspring that are homozygous for many genes may be worse off than individuals that are highly heterozygous for a couple of reasons. First, heterozygosity (having two different alleles for a particular gene) can be beneficial if the two alleles result in the production of two different versions of a protein. For certain genes, producing multiple versions of proteins can be correlated with greater physiological flexibility or improved immune system function. Homozygotes lose this advantage. Second, many harmful versions of genes are recessive or masked by the presence of a healthy version of the gene inherited from the other parent. But an individual that is homozygous for a harmful allele will express the genetic disorder. Examples of human genetic disorders caused by recessive alleles include cystic fibrosis, tay-sachs, and...

Studies with Laboratory Animals Effects of Endocrine Disrupting Chemicals in Plastic

Recent findings include chromosomal damage in developing oocytes in mouse ovaries, and abnormalities in the entire reproductive system in male mice, including a decrease in testicular sperm production and a decrease in fertility, In addition, fetal exposure to bisphenol A increases the rate of postnatal growth and decreases the age at which females mature sexually (go through puberty). These females also have mammary gland abnormalities, and mammary glands appear precancerous by the time the females reach young adulthood. Bisphenol A also causes abnormal brain development, and changes in brain function and behavior. Bisphenol A also disrupts immune function. Bisphenol A is also an animal carcinogen, since exposure to a very low dose during early postnatal development causes prostate cancer in rats.

The Low Dose Issue and InvertedU Dose Response Relationships for EDCs

Foremost among these is a challenge to the operating assumption concerning doses appropriate for toxicologi-cal testing. Focusing on traditional toxicological endpoints, such as gene mutations, weight loss, and death, toxicologists customarily worked at what now are viewed as very high doses, typically in the range of parts per million (ppm) and parts per thousand levels. New data suggest that extremely low doses of EDCs (in the part per billion (ppb) and even part per trillion (ppt) range) can cause measurable and highly significant endocrine disruption. A growing array of studies reveals changes in gene expression, including both gene suppression and gene activation, as a result of low-level exposure to EDCs. For example, recent work on arsenic, long-established to be toxic at high doses, has revealed that at part per billion levels, arsenic can interfere with gluco-corticoid activation of genes involved in the control of metabolism, response to stress, immune function, and the...

Mating and reproduction

The large percentage of the fly's body devoted to reproduction makes clear its importance female flies are essentially ovaries with wings. It is therefore unsurprising that an immune response that might compete for energy would have an effect on reproduction. Even a simple immune response to a non-pathogenic elicitor like E. coli will reduce egg-laying (Zerofsky et al, 2005). Experiments with Salmonella typhimurium strains of various levels of virulence suggest that as pathogenicity increases so egg-laying decreases. In infected females, eggs do not appear to progress beyond stage 8 of oogenesis, when yolk deposition begins (Brandt and Schneider, 2007). It should be unsurprising to the reader at this point in the chapter that this is a checkpoint in egg development that is known to be responsive to insulin signalling (Drummond-Barbosa and Spradling, 2001). A curious phenotype has been observed in male flies linking mating and immunity McKean and Nunney (2001) demonstrated that mating...

Behind and Beyond the Scenarios

Difficulties in 'translating' climatic into health effects are partly due to missing local information, neither provided by climate models nor easily derived fog or haze, storminess, chemical and radioactive load of precipitation, etc. For the longer term, GLAWARS' gravest concern is food supply for survivors. Genuine medical aspects include enteric diseases and those spread by insects or due to poor sanitation and nutrition, all favored in victims who became 'immunocompromised'. The key point here, also identified at the IOM symposium, is just the combined action ofstresses in the nuclear aftermath to impair the immune system. Factors causing immune suppression include radioactive and UV-B radiation, malnutrition, burns and trauma, as well as psychosocial stress. Clinical evidence indicates that these factors all converge in their action on a single element of the immune system, the T-lymphocyte, of which also the 'helper-to-suppressor ratio' is crucial. The Acquired Immune...

Analysis of Infectious Mortality by Means of the Individualized Risk Model

The goal of this chapter is to describe the mechanism underlying the age-specific increase in death risk related to immunosenescence, to determine the cause-specific hazard rate as a function of immune system characteristics. A mathematical model that allows for the estimation of the age-specific risk of death caused by infectious diseases has been developed. The model consists of three compartments (1) a model of immunosenescence, (2) a model of infectious disease, and (3) a model giving the relationship between disease severity and the risk of death. The proposed model makes it possible to analyze age-specific mortality from infectious diseases and to predict future changes in mortality due to public health activity. At the same time it can be used for individualized risk assessment.

Model of Age Related Risk of Death from Respiratory Infections

The principal processes associated with immunosenescence are replacement of naive lymphocytes by memory cells and replicative senescence of lymphocytes. A decrease in the number of naive lymphocytes results in a weak and delayed immune response to new pathogens. Low replicative capacity of lymphocytes leads to a slowed immune response to any challenge as well. The slowed, inadequate immune responses accompanied by widespread damage of target tissues caused by pathogens. Damage of more than a third of vitally important organs (e.g., lung tissue in the case of pneumonia) is related with a high risk of death. The first model, the mathematical model of immunosenescence, describes the age trend of immune system characteristics such as the concentration of naive and memory T cells and their replicative capacity. The model is represented by a system of ordinary differential equations (ODEs). Numerical solution of the system of ODEs yields the sets of immune characteristics for each age....

Reticulate evolution and essential oils

The industrial mint crops are cultivated in several countries for their essential oils. The oil, menthol, carvone, lemoline, dementholated oil and terpene fractions from the latter are variously used in the cosmetics, pharmaceuticals, food, confectionery and liquor industries (Khanuja et al. 2000). The range of medicinal applications of some mints also reflects the diversity of human-utilized products from various members of the genus Mentha. For example, extractions (containing phenols, fla-vonoids, menthol, and menthone) of the oils from peppermint (Mentha piperita) have been shown to have the potential for antimicrobial, antiviral, antioxidant, antitumor, and antiallergenic properties (McKay and Blumberg 2006). In addition, these extracts have the added benefits of (1) producing relaxation of gastrointestinal tissue, (2) analgesic and anesthetic responses in the central and peripheral nervous systems, and (3) modulating effects on the immune system of model animals (McKay and...

Behavioral Adaptations

Apart from herbivores, plants have to face attack by microorganisms. A complex innate immunity system enables them to recognize microbial pathogens and to initiate adequate responses (see Plant Defense). The innate immune system of plants is directed against a broad range of microbes as it recognizes unspecific pathogen-associated molecular patterns, so-called PAMPs. For example, plants recognize the ubiquitous flagellin from microbes via a receptor-mediated process. As a counter-defense, microorganisms evolved so-called effectors that suppress the plant's innate immune system. Some effectors are proteins interfering with the plant's immune perception system and its signaling cascades. The plant pathogen Pseudomonas syringae., for example, introduces more than 30 effector proteins with diverse enzymatic activity into the plant cell. One of these effector proteins is called AvrPto and interferes with the signaling of In humans viruses have the ability to undermine the natural defense...

Physiological Tradeoffs

Deciding whether to invest energy into reproduction or growth is not the only tradeoff that fish face in their energy allocation. Under some circumstances, for example, under heavy size-selective predation, fish might increase their survival more by growing out of the size window of predation than by maintaining investments in the immune system. Fish can thus be thought of as taking a calculated risk by lowering their immune responses in order to grow faster, and although this increases the risk of infections, it may increase overall survival on a longer timescale. Similar physiologically driven tradeoffs exist for example between escapement capability and growth rate.

How do symbionts produce the effects observed

The alternative mechanism by which sym-biont effects on resistance may function is a direct effect. Direct effects could come from secreted molecules that affect the invading species alone. A useful model may be the biology of the gamma proteobacterium Photorhabdus luminescens, which is a nematode-transmitted pathogen of insects. It inhabits nematode guts without pathology. When the nematode host invades an insect, Photorhabdus moves from nematode gut to insect haemocoel. In this latter context, the bacterium is a virulent pathogen, with a formidable array of secreted compounds that protect against the host innate immune system, and which cause active pathology to the host (for instance, through damage to the gut epithelia). Photorhabdus thus demonstrates context-dependent virulence. Change in host species (from nematode to insect) leads to radical change in bacterial behaviour (from commensal to pathogenic).

Additional Microbial Influences

Microbes may influence somatic development. There is a constant conversationbetween host tissues and their symbiotic bacteria during development, with the immune system of the host acting as a key player (McFall-Ngai, 2002). Aside from their profound effect on cockroach development via various nutritional pathways, bacterial mutualists may directly influence cockroach morphogenesis. It is known that gut bacteria are required for the proper postembryonic development of the gut in P. americana (Bracke et al., 1978 Zurek and Keddie, 1996) normal intestinal function may depend on the induction of host genes by the microbes (Gilbert and

Towards a synthetic lifehistory theory of disease pressure in social insects

We therefore submit the hypothesis that, overall, most bee and wasp species have been selected for relatively cheap methods of disease tolerance, whereas the ants and termites have primarily evolved costly mechanisms of colony resistance. The annual bees and wasps may be able to tolerate a fairly high number of diseases of up to moderate virulence, by relying on defences such as individual immune systems, which can be facultatively adjusted according to need, and which are mostly meant to delay the impact of parasites and diseases until the reproductive cycle has been completed. On the other hand, the long-lived fortresses built by ants and termites most probably cannot afford to take such risks once they have grown beyond the colony-founding stage and have thus evolved multiple costly defences to prevent colony infections or to eliminate such infections at an early stage. that perennials are generally more troubled by parasites than annuals, because they are easier to find (a...

Microbes As Pathogens

Blattaria have both behavioral and immunological mechanisms for countering pathogens that successfully breach the cuticular or gut barrier. Wounds heal quickly (Bell, 1990), and cockroaches are known to use behavioral fever to support an immune system challenged by disease. When Gromphadorhina portentosa was injected with bacteria or bacterial endotoxin and placed in a thermal gradient, the cockroaches preferred temperatures significantly higher than control cockroaches (Bronstein and Conner, 1984). The immune system of cockroaches differs from that of shorter-lived, holometabolous insects, and mimics all characteristics of vertebrate immunity, including both humoral and cell-mediated responses (Duwel-Eby et al., 1991). Blaberus giganteus synthesizes novel proteins when challenged with fungi (Bidochka et al., 1997), and when American cockroaches are injected with dead Pseudomonas aeruginosa, they respond in two phases. Initially there is a short-term, non specific phase, which is...

Evolution of Influenza

Influenza is interesting from both epidemiological and evolutionary points of view due to the interplay between genetic changes in the viral population and the immune system of hosts EAR02 . There are two basic hypotheses on how influenza A viruses escape the immune response in host population to cause epidemics (1) antigenic drift, meaning that random point mutations produces novel influenza strains that succeed and persist if they can infect and spread among hosts (2) antigenic shift, meaning that genes derived from two or more influenza strains reassort thus creating a novel descendent genome with a constellation of genes that can infect and spread among hosts. In both The viruses of influenza type A are classified as various subtypes that represent differences in the antigenic reaction of two key glycoproteins hemagglutinin (HA) and neuraminidase (NA). These proteins reside on the surface of the virion. These proteins play key roles in recognition and infection of susceptible...

Symbiosis and immunity

When injected with Escherichia coli, the insect system of cellular and humoral immunity is upregu-lated, and the invading bacteria are killed through phagocytosis, nodulation, and the expression of antimicrobial peptides (AMPs). Removal of elements of this system (e.g. mutations that disrupt the cascade leading to AMPs) is accompanied by sepsis and death in response to challenge. As argued in Chapters 2 and 6 in this volume, the insect innate immune system is a formidable system for protection against natural enemies. Notwithstanding this, insects possess a complex flora of bacterial symbionts. Parasitic symbionts must either not induce cellular and humoral responses, or, if they do induce it, survive this induction. As close antagonists, they may co-evolve with host systems in arms races. Primary symbionts, and secondary symbionts that induce resistance to natural enemies or confer ecological adaptation to host plants, differ from this in that both host and bacteria have an interest...

Is the intracellular location of inherited bacteria key in their ability to live in insects

A pervasive (but possibly unwritten, and indeed potentially misleading) view in the field was that inherited symbionts do not interact with the insect immune system because of their intracellu-lar location. Humoral immunity involves secreted peptides, which are unlikely to be active intracel-lularly. The cascade leading to their production likewise is induced by free bacteria, not bacteria inside cells. Cellular immunity likewise involves recognition of bacteria that are extracellular, followed by their subsequent ingestion and lysis. Infected host cells are not targeted in this process. This makes the intracellular milieu a potential safe haven for bacteria, and it is tempting to suggest that the intracellular environment being a place of safety has in fact the driven the evolution of maternal inheritance for many bacteria. Under this thesis, entry into cells and adopting the intracellular habitat evolved as a way of escaping immune system activity. This entry into cells led to...

Evolution in ecological time

Scientists now agree that evolution can frequently occur over timescales that matter to ecologists, such as a few decades or less. There are few more graphic examples of rapid evolution than of the emergence of new human diseases. In the case of human immunodeficiency virus (HIV), the disease it causes (acquired immune deficiency syndrome or AIDS) was first recognized in 1981. The virus responsible (Figure 8.4) was characterized in 1983 as a retrovirus with similarities to primate lentiviruses, also known as simian immunodeficiency viruses (SIVs). SIVs are widespread among African apes and monkeys, and phylogenetic comparisons of HIV and SIV sequences suggest, with a large margin for error, a likely origin of the current epidemic in the middle decades of the twentieth century (Hahn et al. 2000). Most interestingly, SIVs are not known to cause disease in their hosts, whereas HIVs are, as far as is currently known, 100 fatal. It seems therefore that HIVs have evolved to become more...

Phylogenetic Approaches to Influenza Type A

Phylogenetic analysis of seasonal influenza sequence data has been used to classify nucleotide substitution mutations. In many codons of the HA gene mutations that produce a change in protein sequence are more frequent than those that do not BU99 . This finding indicates that selective pressures imposed by the immune system of the hosts can drive the evolution of some codons of HA. Thus an evolutionary perspective can illuminate functional studies of infectious disease EAR02 .

Many inherited bacteria can be found outside of cells in a hostile immune environment

Immune system It is, in fact, commonly observed that many symbionts have both intra- and extracellular phases (Moran et al., 2005b), in some cases moving outside of cells during certain life-history phases. Other microbes that are maternally inherited symbionts, such as Arsenophonus, have an extracellular location (Huger et al., 1985). These observations indicate that many symbionts are found outside cells at some point in their life history, and that this will lead to them being exposed to interaction with the host immune system. For parasites, avoidance of immune system activity must be a property of the bacterium. For beneficial symbionts, which the host has an interest in maintaining, it may be a property of the bacterium, the host, or both.

Large Scale Phylogenetic Analysis of HA

As noted, phylogenetics have been widely used to understand history of influenza epidemics, host shifts, as well as evolutionary interactions with the hosts immune system (see Sect. 2.3.1). However, most phylogenetic analyses of influenza thus far have used only fractions of the dataset of influenza nu-cleotide sequences in the public domain. The sequences in the public domain are largely HA, but recently whole genomes have been produced. The Institute for Genomic Research (TIGR) is rapidly sequencing and releasing into the public domain thousands of influenza genomes under the Microbial Sequencing Center (MSC) program sponsored by the National Institute of Allergy and Infectious Disease (NIAID) GHE05 . St. Jude Children's Research Hospital in Memphis has contributed a significant increase in the number of avian influenza genomes sequences 0BE06 .

Bacterial mechanism of immune avoidance

There are two types of solution to the 'problem' of the host immune system. The first is to limit the time spent outside of cells. The second is to evolve mechanisms that either stop induction of host immunity, or be insensitive to the host systems. The 'lack of coat' explanation for failure of spiroplasmas to elicit an immune response is a conjecture. It is unlikely to be generally true of haemolymph-associated bacteria, as Arsenophonus, Serratia, Hamiltonella, and Sodalis are all gamma proteobacteria likely to carry significant cell walls, just as Photorhabdus does. Whereas alteration of The genomes of these bacteria do suggest some candidate molecules for interaction with the immune system. The genome of A. nasoniae, for instance, possesses a homologue of ecotin, within the operon of a type-three secretion system (making it highly likely to be a secreted peptide) (T. Wilkes, A.C. Darby, and G.D.D. Hurst, unpublished results). Ecotin encodes a protein belonging to the serine...

Immunity and Vaccination

Immunity (the ability to resist infection based on mobilization of the immune system) to many diseases can result from a prior infection of the same agent. Getting the measles, for example, protects the host from being infected again later. Thus, a person can contract many diseases only once. Colds and influenza, on the other hand, stem from viruses that continue to produce new strains that avoid the body's predeveloped defenses, so that they may be contracted repeatedly. Prior exposure also does not protect against many microbial toxins, such as those involved in botulism food poisoning or against some parasitic infections, such as schistosomiasis, tapeworm, and athlete's foot. In some cases, the immune system can be helped by injection of an immune globulin, or antibody. Approved immune globulins are listed in Table 12.9.

Aging and nosocomial infections

The aging of the population represents another factor driving the nosocomial infection epidemic. While in 1900 only 1 percent of the world's population (15 million people) was greater than 65 years of age, by 1992 this proportion had grown to 6 percent (342 million people). By 2050, it's estimated that 2.5 billion world inhabitants will be older than 65 (Strausbaugh, 2001). Several factors may increase elderly patients' risks of acquiring HAIs. Their immune function and natural defenses may be decreased. Older patients have less robust T-lymphocyte proliferation, leading to decreased antibody production and cell-mediated immune function with increasing age. Conditions more prevalent in the elderly, such as diabetes, malignancy, vascular disease, and dementia, also may decrease barriers to infection. Functional incapacity due to aging may necessitate use of invasive devices, such as urinary catheters or feeding tubes, which further bypass the body's natural defenses. Incapacity and...

Effect of PDVs on host haemocytes

Three main immune responses implicating haemo-cytes have been described in Lepidoptera. Phagocytosis corresponds to the engulfment of bacteria or yeast by individual cells, whereas nodulation and encapsulation involve haemocytes that will respectively, surround masses of bacteria or nec-rotic tissues, or form capsules around larger targets such as parasitoid eggs. Four circulating haemo-cyte types have been described in Lepidoptera and have been shown to be implicated in these cellular immune responses (Ribeiro and Brehelin, 2006). Plasmatocytes and granular cells are numerically the two main classes of haemocytes, accounting for 85-95 of all the haemocytes in a caterpillar (Loret The pathologies induced by MdBV on the haemocytes of two lepidopteran hosts, P. inclu-dens and H. virescens, were compared to those observed upon injection of bracovirus particles from M. mediator (MmBV) and Microplitis cro-ceipes (McBV) (Kadash et al., 2003). Interestingly the effects induced by the three...

Effort and Investment

Does the high energy expenditure ofprovisioning necessarily come at some life history cost Specifically, does today's provisioning reduce a provisioner's survival or fecundity Much ofthe literature on social insects makes little use of these concepts, but many avian studies have attempted to document future costs of reproduction, though with mixed results. Martins and Wright's (1993b) study of swifts provides an example. Like the parents in many other avian studies, swifts worked harder in response to increased demand, whether experimentally (brood size manipulation) or environmentally (bad weather) imposed. In some studies, avian parents sustained a higher workload for a considerable period. Social insects show similar responses when challenged in analogous experiments (Fewell and Winston 1992). Both groups of organisms often show short-term changes in body weight, condition, immune system traits, or the size ofstored reserves in response to the challenge. But most studies have...

Cumulative effects of PDVs and other virulence factors on host immunity

PDVs constitute a component of the parasitoid arsenal to overcome the host immune response of M. demolitor, which amplifies the effects of MdBV on the immune system and the development of the host P. includens (Strand, 1994). In most ichneumo-nid wasps, PDVs and venoms appear to act independently (Stoltz and Guzo, 1986 Asgari, 2006).

Modeling infection with accidental pathogens

Only when we include another finding of the biology of the meningo-coccus in the modeling of its epidemiology can such clustered outbreaks be obtained. Namely, it is necessary to take into account that the bacteria are are highly mutating easily mutate and evade the hosts' immune system during harmless carriage.27 The different mutants of the bacterium have different likelihoods accidentally harming their host by causing severe disease. Hence in the simplest modeling set-up where we found clustered outbreaks17 we distinguished between harmless infection never causing disease, the I class, and potentially harmful infection with a different mutant strain of the bacteria, the Y class, from which with a small rate e, the pathogenicity, disease cases X are created. For pathogenicity close to its critical value of zero we found huge fluctuations, to be expected from the theory of critical phenomena in physics of condensed matter9'28 and in biology of critical birth and death processes7'8...

The consequences of host reaction SIR

The variations in mechanisms used by different types of organism to fight infection are clearly interesting and important to parasitologists, medics and veterinarians. They are also important to ecologists working on particular systems, where an understanding of the overall biology is essential. But from the perspective of an ecological overview, the consequences for the hosts of these responses are more important, both at the whole organism and the population levels. First, these responses determine where individuals are on the spectrum from 'wholly susceptible' to 'wholly resistant' to infection - and if they become infected, where they are on the spectrum from being killed by infection to being asymptomatic. Second, in the case of vertebrates, the responses determine whether an individual still expresses a naive susceptibility or has acquired an immunity to infection.

Immunity and resistance

Mosquitoes can block this development with a variety of immune responses by lysing the ooki-netes as they are migrating through the midgut wall (Vernick et al., 1995), by producing nitric oxide (Luckhart et al., 1998) (which impedes the development of the parasite), by melanizing ookinetes and early oocysts (Collins et al., 1986), and by killing parasites with antimicrobial peptides (Dong et al., 2006). Extensive studies in molecular biology have In the context of this chapter, there are two striking features of these molecular studies. First, functional immunity depends on a large number of genes and, in particular, on the interaction between genes. For example, knocking out either one of two receptor genes (CLIP A2 or CLIP A5) roughly halves the number of oocysts in a midgut, knocking out both decreases the number by a factor of close to 10, and knocking out an additional one (CLIP A8) brings the number back up to about a third of the unmanipulated controls (Volz et al., 2006)....

Exploitation of Microalgal Products

Various unsaturated fatty acids in microalgal biomass are important as dietary supplements to prevent various diseases (e.g., high plasma cholesterol, hypertension, etc.) and to boost the immune system. Microalgal biomass also contains all the important vitamins, especially the B1 B2, and C vitamins and nicotinic acid. The variety of carotenoids is greater than in higher plants - -carotene, lutein, violaxanthin, zeaxanthin, neoxanthin, etc. Among them, the oxygenated xanthophylls, astaxanthin and Microalgal polysaccharides are pharmacologically important. For example, certain highly sulfated polysac-charides trigger either a cellular or humoral stimulation of the human immune system. Effective polysaccharide fractions have been found mainly in cyanobacteria however, compounds from green and red algae are also efficient.

Nutrient dynamics and immune defense by hosts

Since parasitoids and pathogens are often the most important mortality factors facing insects, immune defense has long been recognized as a critically important maintenance function (see Chapter 14 by Kraaijeveld and Godfray). Investment in defense also has possible fitness costs and trade-offs with reproduction and other needs. Such trade-offs have been viewed as either a plastic response, usually referred to as the cost of using the immune system or as a co-evolved trait viewed as the cost of having an immune system (Schmid-Hempel & Ebert 2003, see also Chapter 14 by Kraaijeveld and Godfray). The innate immune response of insects consists of both cellular and humoral components (Strand & Pech 1995, Lavine & Strand 2002, Hoffmann 2003). Some defenses, like melanization, are non-specific and have activity against a range of parasites, while other defenses are directed to a restricted set of parasite species or types. The primary defense response against parasitoids is...

Factors affecting microparasite population biology

The course of an infection includes a latent period after exposure to the source of the infection. During this period the virus, for example, will increase exponentially. The next stage includes the infectious period, during which time the host develops the symptoms of the disease. Meanwhile, as the parasite population is building its numbers, the host immune system begins developing specific antibodies. As the antibody numbers increase, the parasite population plummets and the symptoms of the illness subside. The host ceases to be infectious at some point during the illness and the previously susceptible individual passes from S (susceptible) to I (infected) to R (recovered and immune). Of course some infected individuals may die during the course of the disease, and some recovered individuals may eventually lose their immunity. Other important factors affecting the natural history of the infection include the length of the infectious period, the time-lag derived from the latent...

Is resistance affected by nutrient dynamics

Evidence that immune defense is energetically expensive in insects and other organisms derives from the observation, in diverse species, that activation of the immune response Other evidence for the energetic cost of immune defense stems from the observation that stress, including high temperature, starvation, or persistent infection, increases susceptibility to infection due to a presumed reduction in resources available for immunity (Bouletreau 1986, Feder et al. 1997, Faggioni et al. 2000, Yang & Cox-Foster 2005). Insect resistance to parasitoids can also vary by age with younger larvae or older adults usually being most susceptible to infection (Salt 1970, Washburn et al. 2001, Hillyer et al. 2005, Zerofsky et al. 2005). This increased susceptibility could be due to age-dependent changes in the function of the immune system, lower nutrient reserves for investment in defense, or both.

Effects on Fitness and Ecological Parameters

Organisms because they may affect organismal-level fitness components. This may be translated into effects on populations, and eventually communities and ecosystems. This is illustrated in Figure 8. First, because DNA damage and mutations can lead to cell death and cancer, this may affect survival. Because DNA damage enhances the rate of cell senescence, accumulation of unrepaired damage and mutations may affect longevity and population age structure. DNA damage and mutations have their greatest deleterious effect on rapidly dividing cells. Because gonadal germ cells are rapidly dividing, they are particularly susceptible to the effects of DNA damage and mutations. Growth may also be affected because of induced cell death, interference with DNA replication, or induced delay of cell division (DNA damage induces cell cycle delay, a phenomenon that halts the cell cycle to allow time for repair before DNA replication or mitosis). Immune cells, both mature white blood cells and white blood...

Discussion of Key Questions

As a result of this research, PCBs have been labeled probable human carcinogens by the EPA, and are also suspected of inducing developmental and learning disorders, impairing human immune systems, andcausinglowbirth weights. Production of these chemicals hasbeenbannedinternationally under terms of the United Nations' recent treaty on Persistent Organic Pollutants (see http www.

Nitrogen Toxicity in Aquatic Ecosystems

A more toxic component is the nitrite ion, NO-. NO- in water forms a chemical equilibrium with nitrous acid (HNO2) NO- 4 H4 HNO2. Both forms can be directly toxic to organisms, but the equilibrium strongly depends on pH and, in general, NO2- is a more common form than HNO2. As with NO-, NO- strongly affects the oxygen-carrying capacity of organisms. In addition, NO2- is known to cause electrochemical imbalances in the cells, membrane malfunctions, and repression of the immune system. In high concentrations (> 0.25 mgl-1), NO- is toxic, and crustaceans (decapods, amphipods), insects (ephemeropterans), and fishes (salmonids) are among the most vulnerable groups. Since chloride (Cl-) ions are taken up by fish via the same mechanisms in their gills, Cl- uptake inhibits NO-uptake and protects the fish against NO- toxicity. Seawater therefore reduces the toxicity of NO- considerably. NH3 mainly affects biota close to point sources such as agricultural and industrial effluents or sewage...

The Argument and Its Limits in Brief

Once yellow fever and malaria became common in the Americas, differential immunity gave both diseases political importance. They made it extremely hazardous for outsiders with unprepared immune systems to come to the Greater Caribbean, which in practice mainly meant people from Europe and North America. The hazard escalated if they came in large groups for reasons addressed in Chapter 2. Large-scale settlement schemes, such as those at Darien and Kourou (Chapter 4) routinely collapsed amid searing epidemics. Large-scale military expeditions usually met the same fate. Before 1800, the great powers tried to take strategic or wealthy colonies from one another whenever suitable opportunity arose. Spanish possessions were especially favored targets because Spain (after 1580 or so) often appeared weaker than its rivals, and because its assets in the Americas, notably its silver mines, seemed especially worth taking. But by relying heavily on locally recruited men and on fortifications of...

Microarrays can indicate costs of immunity

In many of the transcriptomic experiments, gene expression is measured along a time course after infection to include various stages of the immune response. In addition to the putative immunity genes, this can also provide information on genes that reflect the costs of launching an immune response. Most genes with differential expression after parasitoid attack were not exclusively expressed (or switched off) during the immune response, but the expression was changed relative to the (unparasitized) controls (Wertheim et al, 2005). The continuous expression of all these genes in unparasitized samples implies that the immune response consists at least partially of a modulation of other ongoing developmental and metabolic processes. These expression data provided some evidence that such modulation may incur some costs. A suite of metabolic genes was down-regulated during the immune response, and these genes shared the same over-represented TFBM in the upstream regions as some suites of...

Effects on Particular Organs or Organ Systems

Immune System The immune system consists of various organs, including the bone marrow, spleen, thymus, and lymph nodes, plus specialized cells and plasma proteins produced by those organs which circulate in the blood and lymphatic system. The cells are the lymphocytes, or white blood cells, and include T cells and B cells. The proteins include the immunoglobulins, interleukins, and the complement system. Together they act to rid the body of chemical and biological contaminants. There are three types of immune system derangements. Immunosuppressants reduce immune response and render the body more vulnerable to foreign substances. Immunostimulants cause hypersensitivity reactions or allergies. Autoimmune disease is the condition where the immune system attacks its own substances as if they were foreign. Immunostimulants usually cause their reaction within 15 minutes of exposure. A first exposure does not cause a reaction since the immune system must generate immunoglo-bulin antibodies....

What Is Plant Defense

In addition to constitutive defense, plants can respond both at the point of attack and via a systemic response. The signal and receptor mechanisms in the inducible defensive system of plants are as complex and sophisticated as the signaling mechanisms in animals. But plants do not have a circulatory system. However, cells are linked via the plasmodesmata, a membrane-lined channel in the cell walls, which is large enough for travel of small molecules (mass of < 1000 Da). Thus, in contrast to the circulating cells of the immune system of multicellular animals, the signal and response mechanisms of plants rely on production of chemicals and movement of those to other cells via cytoplasmic channels between cells, intercellular spaces, and the vascular system, which in turn can trigger further production of chemicals by cells receiving the signals. Plants have a hypersensitive response, which is not enemy-specific and results in cell

Eco Semiotic and Cognitive Landscape

Recently Kull et al. (2008) discussed the necessity to introduce a bio-semiotic approach to the study of the living systems. In particular they individualized important compartments of biology in which the bio-semiotic approach is important like animal communication, bio-semiotic processes in ecosystems (plant-pollinator interaction), the immune system, and neurosemiotics, etc.

Effects of PCBs on Populations

In 1988 and 2002 common (harbor) seals in the North Sea suffered dramatic epizootics of phocine distemper virus (in 1988 around 50 of the Western Atlantic population died). The seals were found to contain high concentrations of PCBs and other organo-chlorine pollutants, and there is a suspicion that these chemicals may have suppressed the seal immune systems, making them more susceptible to the phocine distemper virus. No definite link between PCB exposure and the epizootics has been proven.

Common Biological Responses

Biological effects of exposure to PAHs are diverse. These compounds are known to affect the immune system, impair growth and reproduction, cause tumor formation, and of course lead to death if concentrations are high. Some of the known responses are discussed below. Toxicity values are generally highly variable among species and compounds. This is primarily a result of the inherent toxicity of compounds, species susceptibility, the length of time for exposure, and the uptake and elimination kinetics (toxicokinetics) found among species. A brief general description of the observed toxicity values are presented here, with additional detail for the most

Constitutive versus induced defense

Plants usually produce a certain quantity of a chemical defense, a sort of background amount. This is called a constitutive defense. After a plant is attacked, however, the amount of these chemicals usually increases. In other cases, entirely new compounds are produced after an attack. Such a reaction, known as an induced defense to herbivore attack, can be thought of as a parallel to the immune system in animals.

Management of overabundant populations

An immunocontraceptive vaccine causes an animal's immune system to produce antibodies that prevent fertilization, with possibly fewer side effects than steroid hormones. R. A. Fayrer-Hosken and a support team have recently carried out trials at Kruger on 41 adult female elephants identified as nonpreg-nant with a vaccine developed from the pig's zona pellucida (PZP). Of these elephants, 21 were initially vaccinated, while the other 20 controls received a placebo. All elephants were fitted with radiotransmitters for subsequent monitoring. The vaccinated elephants received booster doses after 6 weeks and 6 months. A year later, 19 of the treated elephants were recaptured and scanned by ultrasound for pregnancy of these, 9 (47 ) were pregnant. By contrast, 16 (89 ) of the 18 control elephants that were recaptured were pregnant. In a new set of experiments, 10 elephants received the initial vaccination followed by boosters 2 or 4 weeks later. Only 2 (20 ) of these 10 elephants were...

Box 141 Concepts and caveats

Specificity is a quantitative measure, and discrimination of parasites by the immune system can take place on different levels of parasite relatedness. Specificity can be coarse-grained, for example between general classes of microbes, such as bacteria and fungi. This coarse specificity can be explained by differential effectiveness of pathways that are already relatively well understood (e.g. Toll and Imd). However, at the discriminative extreme of the specificity spectrum is the differentiation between strains of the same parasite species. Some of the examples given in this chapter suggest that the insect immune system can act on this level of specificity. This suggests that it is necessary to look beyond the currently well-studied mechanisms for the mechanistic basis of immune specificity in insects (see Chapter 5 in this volume). The evolutionary consequences of immune specificity will also depend on the level at which it acts. For example, selection for diversity of parasite...

Empirical evidence for specificity and specific interactions

Of immune defence pathways, and their importance for combating pathogens. For instance, a plethora of work on Drosophila using mutants of certain immune system components has demonstrated specificity on a coarse level. Particular sets of recognition, signalling, and effector molecules are required for defence against certain classes of microbes but not others (Hultmark, 2003). For example, the two best-studied signalling pathways in Drosophila immunity, Toll and Imd, have been shown to be differentially required for an effective immune response depending on the microbe in question (Hultmark, 2003). Furthermore, post-genomic studies show different patterns of gene expression on exposure to distinct pathogens and parasites. When Drosophila received a fungal, protozoan, viral, or bacterial infection, 64 of the upregulated genes were specific to the infection type (Roxstrom-Lindquist et al., 2004). Further evidence concerning the differential use and importance of immune system...

Immune priming as a specific response to the current environment

The observation of specific immune responses, specific interactions between host and parasite types, and the rapidly accumulating knowledge on the molecular mechanisms of the insect immune system (Chapters 2, 4, and 5 in this volume Du Pasquier, 2005 Dong et al, 2006) collectively suggest that the insect immune system is much more sophisticated in its performance than was traditionally believed. Two additional responses are particularly interesting in the context of specific responses. These are immune priming across generations (trans-generational immune priming) and immune priming within an individual. These two phenomena are based on immune priming that is, the capacity of generating an improved immune response depending on previous experience with the environment (Figure 14.1b and 14.1c).

Behavioural mechanisms

There are a number of behavioural mechanisms that insects could employ to reduce their probability of becoming exposed to parasites and pathogens, and to ameliorate their effects should they become infected. These include mate selection (to avoid parasites that are transmitted by potential sexual partners) selective diet choice (to avoid ingesting parasites) avoiding or dispersing from areas of high infection risk social behaviours and group-living (to take advantage of 'dilution effects') self-grooming and reciprocal allogrooming (e.g. to remove fungal spores or ectoparasites) behavioural fever and chills (i.e. altering body temperature to reduce parasite fitness and or to increase immune function efficacy) and oral self-medication (i.e. ingesting nutrients that enhance physiological immunological resistance mechanisms). Some of these behavioural mechanisms are reviewed here.

Mate choice and promiscuity

This is because a recent study on the mealworm beetle (Tenebrio molitor) has shown that, in both sexes, mating reduces the activity levels of phenoloxidase, a key enzyme in the insect immune system (Rolff and Siva-Jothy, 2002) (see below). This mating-induced downregulation of immunity lasts for at least 24 h and appears to be mediated by juvenile hormone. Thus, by mating frequently, individuals may be compromising their immune systems. Similar conclusions were reached in an earlier study by McKean and Nunney (2001) using the fruitfly Drosophila melanogaster (Fig. 10.2). They found that as the number of females housed with each male was increased (from 0 to 4), so there was a highly significant decrease in the male's ability to immunologically clear an experimental injection of E. coli bacteria. This reduced immunocompetence was not due to food shortage, since it was prevalent also when food was in excess. Nor was it simply due to crowding effects, since males housed with four males...

The consequences of immune priming within and across generations

The demonstration in insects of specific immune priming and trans-generational immunity suggest that while they rely on different mechanisms, the immune systems of both vertebrates and invertebrates have been selected by parasites and pathogens to perform similar functions. It is likely that a particular level of spatial and temporal variation in exposure to parasite types would give a benefit of immunity that is acquired depending on prior experiences. For immune priming to be beneficial variation in the exposure to parasite types should be rapid enough to stay ahead of changes The existence of immune priming both within individuals and across generations will have implications beyond that of understanding the evolution of immune system function. Once they have evolved in hosts, these phenomena of immune priming would have a set of consequences for the further evolution of hosts and parasites, and the co-evolutionary interactions between the two. While this area has received little...

Synthetic paints and varnish

Additives used in PVAC products often include sulphonamides, which can damage the immune system, and alkylphenol ethoxylates such as nonylphenol which are thought to be environmental estrogens. Acrylate monomers can cause eczema through contact with wet paint. Many of the paints can emit volatile compounds for long periods after painting is complete, such as excess monomers of acrylates, styrene, softeners (e.g. phthlates) and fungicides. Several of these can stimulate hypersensitive reactions and lead to allergies. The emissions diminish with time, depending upon the temperature, the moisture situation and the thickness of the paint. After a year most of the emissions cease.

Immunological mechanisms

One of the advantages of examining evolutionary questions about immunity using insects is that the insect immune system is simpler than its vertebrate equivalent, in that it lacks an adaptive or acquired immune system (in the conventional sense but see below). There are many similarities between the vertebrate and invertebrate innate immune systems, and this makes insects potent models for understanding innate immunity (Vilmos and Kurucz, 1998). Even so, the insect innate immune system is still not fully understood and there remain gaps in our knowledge concerning the relative importance of its different components and how they interact. The immune defences of insects include constituitive and inducible defences, and both cellular and humoral components figure prominently. They include cell-mediated responses, such as nodulation, phagocytosis, and cellular encapsulation the enzymes of the prophenoloxidase cascade and inducible antimicrobial peptides (including lysozymes, attacins,...

Reticulate evolution and protozoan pathogens

Infections of protozoan parasites affect a large proportion of H. sapiens individuals. For example, > 1 million people are infected with Toxoplasma gondii (Boyle et al. 2006), with Toxoplasmosis (the disease caused by T. gondii infections) accounting for the third highest number of food-related fatalities in the United States (http www.cdc.gov toxoplasmosis). Furthermore, members of the protozoan genus Cryptosporidium cause the diarrheal disease, Cryptosporidiosis. Over the past 20 years, Cryptosporidium infections have become one of the most frequent causes of waterborne disease (both from recreational and drinking water supplies) in the United States. Furthermore, Cryptosporidium and people burdened by its infections are present throughout the world. Many protozoan infections have a limited mortality rate among otherwise healthy humans, because their immune system is capable of ridding their bodies of the pathogen (Fricker et al. 1998). However, with the growing percentage of the...

The bedbug and traumatic insemination

Male bedbugs breach the female's cuticle during copulation and inseminate directly into the female's haemolymph (Usinger, 1966), a mode of insemination that has been shown to be potentially very costly to females (Stutt and Siva-Jothy, 2001). Since the male inserts his aedeagus directly through the female's abdominal cuticle and inseminates into the haemocoel, rather than use the genital tract (Carayon, 1966), any surface microbes (Reinhardt et al., 2005) will be introduced directly into the body cavity. Moreover, this will occur with the simultaneous introduction of a large number of sperm, another form of non-self as far as the female's immune system is concerned. Reinhardt et al. (2003) experimentally revealed that the septic consequences of traumatic insemination formed a large part of the cost base identified by Stutt and Siva-Jothy (2001). Interestingly, male bedbugs direct their mating efforts at females only if they have recently fed (Siva-Jothy, 2006), probably because...

Physiological consequences of mating on immunity

Recent studies have shown that mating induces downregulation of immune function in males and females (e.g. Siva-Jothy et al., 1998 McKeen and Nunney, 2001), which does not appear to be caused by energetic demands. Whereas it is possible that the effects in McKeen and Nunney's (2001) study were linked to the copulatory wounding processes identified by Kamimura (2007), that seems unlikely in Siva-Jothy et al.'s (1998) study (however, the aedeagi of odonates are known to bear recurved spines that function in sperm competition (Corbet, 1999) and might therefore damage the female's genital tract). A physiological candidate for generating mediating the observed reduction in immune function is juvenile hormone (e.g. Zera and Harshman, 2001) and Rolff and Siva-Jothy (2002) revealed that the endogenous release of this hormone stimulated by mating was responsible for reducing immune function after mating. Whereas immune and juvenile hormone function are conserved across insects, it is likely...

Male compounds that may affect female immunity

Male insects are known to transfer compounds in their seminal fluids that affect female receptivity (e.g. Thornhill and Alcock, 1983), oviposition rates, and longevity (e.g. Chapman et al., 1995). Given that these physiologically active compounds affect a complex range of female traits it is likely that they may coincidently, or deliberately, enhance reduce female immune function. For example, it has been established that male Drosophila transfer three different antimicrobial peptides in their seminal fluid (Lung et al., 2001) as well as transfer compounds that activate phenoloxidase in the female's genital tract (Asada and Kitagawa, 1988). These male-transferred compounds may function primarily to protect and or enhance the competitiveness of the male's ejaculate, but may have the correlated effect of protecting the female and or reducing her immune costs as well. We know almost nothing about the immuno-logical function of insect seminal fluid and or why males transfer these...