The imd gene is required for local Cecropin expression in Drosophila barrier epithelia

Surfaces of higher eukaryotes are normally covered with microorganisms but are usually not infected by them. Innate immunity and the expression of gen e-encoded antimicrobial peptides play important roles in the first line of defence in higher animals. The immune response in Drosophila promotes syste mic expression of antimicrobial peptides in response to microbial infection . We now demonstrate that the epidermal cells underlying the cuticle of lar vae respond to infected wounds by local expression of the genes for the ant imicrobial peptide cecropin A. Thus, the Drosophila epidermis plays an acti ve role in the innate defence against microorganisms. The immune deficiency (imd) gene was found to be a crucial component of the signal-induced epide rmal expression in both embryos and larvae. In contrast, melanization, whic h is part of the wound healing process, is not dependent on the imd gene, i ndicating that the signalling pathways promoting melanization and antimicro bial peptide gene expression can be uncoupled.