Microbial infection or exposure to bacterial pep-tidoglycan induces synthesis of lysozyme and antibacterial peptides that are secreted into M. sexta plasma (Dunn et al, 1985; Kanost et al., 1988). Lysozyme (Mulnix and Dunn, 1994; Lopez-Zavala et al, 2004) and antibacterial peptides from the cecro-pin, attacin, moricin, gloverin, and lebocin families (Dickinson et al, 1988; Kanost et al, 1990; Zhu et al, 2003a; Dai et al, 2008) from M. sexta plasma have been investigated by biochemical and DNA cloning methods. They are synthesized by the fat body within a few hours of bacteria being injected, and can remain at high concentrations in plasma for 2-3 days, providing strong protection against bacterial growth in the haemocoel (Tzou et al, 2002; Eleftherianos et al., 2006a). Lysozyme hydrolyses peptidoglycan in bacterial cell walls, which causes bacterial lysis. In addition, the liberated peptidoglycan fragments serve as signals to promote induced expression of immune genes and phenoloxidase activation (Kanost et al, 1988; Wang et al, 2006; Park et al, 2007; Kim et al, 2008). These antibacterial factors are also present in M. sexta eggs, which can synthesize antimicrobial peptides in response to bacteria (Gorman et al., 2004). High concentrations of lysozyme and other antibacterial proteins are also secreted into the midgut lumen during metamorphosis (Dunn et al., 1994).
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