Antimicrobial peptides from insects with special reference to silkworm Bombyx mori L: A review

A characteristic of insect immunity is the rapid and transient activation of immune genes to produce effectors in response to microbial infections. The production and release of antimicrobial peptides (AMPs) are thought to play a major role in the innate immunity against invading pathogens. The antimicrobial peptide genes are induced by microbial challenge in the fat body (equivalent of the mammalian liver), followed by the secretion of these peptides into the haemolymph, which is the hallmark of the humoral reactions. These antimicrobial peptides from several families reach high concentrations in the haemolymph and efficiently kill invading microorganisms. Antimicrobial peptides (AMPs) are low molecular weight biologically active molecules having exciting properties. A wide variety of AMPs have been isolated from various sources like plants, animals, mammals, insects and microorganisms. The most familiar structure is represented by α-helical conformation in organic solutions or disulfide stabilized β-sheet with or without α-helical domains present. Despite of striking diversity in structure and chemical nature, all of them possess antimicrobial activity. This fundamental property makes them as a promising candidate compared to chemical antibiotics. In the near future attempts should be made to generate AMPs with higher antimicrobial activity and broad range of microbe action. In this review, focus is given on the AMPs found in the silkworm Bombyx mori, with some findings on the innate immunity responses (both cellular and humoral). This review also summarizes six classes of antimicrobial peptides (cecropin, defensin, attacin, leboncoin, moricin and gloverin) found in B. mori and their mode of actions against diverse range of pathogenic microbes.