text: Imd signalling regulates a number of effector peptides and proteins that are produced en masse following immune challenge. This includes many of the major antimicrobial peptide genes of Drosophila, particularly: Diptericin, Attacin, Drosocin, Cecropin, and Defensin. The Imd pathway regulates hundreds of genes after infection, however the antimicrobial peptides play one of the most essential roles of Imd signalling in defence. Flies lacking multiple antimicrobial peptide genes succumb to infections by a broad suite of Gram-negative bacteria. Classical thinking suggested that antimicrobial peptides worked as a generalist cocktail in defence, where each peptide provided a small and somewhat redundant contribution. However Hanson and colleagues found that single antimicrobial peptide genes displayed an unexpectedly high degree of specificity for defence against specific microbes. The fly Diptericin A gene is essential for defence against the bacterium Providencia rettgeri (also suggested by an earlier evolutionary study). A second specificity is encoded by Diptericin B, which defends flies against Acetobacter bacteria of the fly microbiome. A third specificity is encoded by the gene Drosocin. Flies lacking Drosocin are highly susceptible to Enterobacter cloacae infection. The Drosocin gene itself encodes two peptides (named Drosocin and Buletin), wherein it is specifically the Drosocin peptide that is responsible for defence against E. cloacae, while the Buletin peptide instead mediates a specific defence against another bacterium, Providencia burhodogranariea. These works accompany others on antimicrobial peptides and effectors regulated by the Drosophila Toll pathway, which also display a specific importance in defence against certain fungi or bacteria.
  This work on Drosophila immune antimicrobial peptides and effectors has greatly revised the former view that such peptides are generalist molecules. The modern interpretation is now that specific molecules might provide a somewhat redundant layer of defence, but also single peptides can have critical importance, individually, against relevant microbes.