Drosophila antimicrobial peptides

Insects are remarkably resistant to microbial infections. Their host defense relies on cellular and humoral responses. The cellular mechanism involves phagocytosis and encapsulation of pathogens. The humoral response includes activation of proteolytic cascades leading to coagulation and melanization and synthesis of antimicrobial pep tides acting in the hemolymph to fight the infection. Over the last years, Drosophila melanogaster has become a favourite model to investigate the molecular mechanisms of insect immunity. In Drosophila seven distinct molecules plus isoforms have been characterized, the antibacterial peptides cecropins, defensin, drosocin, diptericin and attacins, the antifungal drosomycin and metchnikowins which are active against both bacteria and fungi. These molecules belong to the 4 families of insect antimicrobial peptides namely (1) peptides forming a helices, (2) cysteine-rich peptides, (3) proline-rich peptides and (4) peptides with a high content in glycine residues. These antibiotics have in common a positive net charge which allows them to interact with the membrane of the microorganisms. nisms. In response to an experimental infection, the overall hemolymph concentration of Drosophila antimicrobial peptides synthesized by the fat body (a functional equivalent of the mammalian liver) reaches the value of 200 mu M, half of which is accounted for drosomycin. Recent studies on the regulation of the antimicrobial peptide gene expression during the systemic Drosophila immune response has revealed striking similarities with vertebrate innate immunity.