Sperm as nonself

Female vertebrates are faced with an immunological dilemma upon receiving their mate's gametes: sperm are non-self. Whereas this is also true for female insects, they (a) do not possess the sophisticated allograft-recognition mechanisms of vertebrates and (b) usually maintain sperm in a cuticle-lined structure(s). Consequently, there are unlikely to be any direct immunological consequences of having to deal with allogenic cells. However, cimicid females are faced with this situation since sperm are injected directly into the haemocoel and must swim through the haemolymph to reach the ovaries (Usinger, 1966). The females of C. lectularius, and other cimicids, are known to use their haemocytes to phagocytose sperm (Carayon, 1966), although it is far from clear whether this is an immunological response to the detection of 'non-self', the removal of dead or dying cells from the haemocoel or, as suggested by Eberhard (1996), a mechanism to select the sperm of desirable males.

Almost no work has been done to examine the immune consequences of storing and maintaining non-self cells in insects (or, for that matter, in vertebrates) despite the fact that female insects often do this for prolonged periods. In most insects this is unlikely to be problematic since there is a cuticular haemocoel/gential-tract barrier and insects appear to have weakly developed allograft-recognition systems (Chapman, 1998). However, a recent study of vertebrate antimicrobial peptides revealed that these compounds can immobilize sperm in the female genital tract (Reddy et al, 2004). I am not aware of any studies that examine the interplay between insect immune effector compounds and sperm function/survival in the female's genital tract, but suspect that the wealth of female genital-tract accessory glands in insects will reveal some interesting immunological phenomena in relation to the female's interaction with sperm.

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