Drosophila immunity: Genes on the third chromosome required for the response to bacterial infection

We have screened the third chromosome of Drosophila melanogaster for mutati ons that prevent the non-nal immune response. We identified mutant lines on the basis of their failure to induce transcription of an antibacterial pep tide gene in response to infection or their failure to form melanized clots at the site of wounding. These mutations define 14 genes [immune response deficient (ird) genes] that have distinct roles in the immune response. We have identified the molecular basis of several ird phenotypes. Two genes, s cribble and kurtz/modulo, affect the cellular organization of the fat body, the tissue responsible for antimicrobial peptide production. Two ird genes encode components of the signaling pathways that mediate responses to bact erial infection, a Drosophila gene encoding a homolog of I kappaB kinase (D mIkk beta) and Relish, a Rcl-family transcription factor. These genetic stu dies should provide a basis for a comprehensive understanding of the geneti c control of immune responses in Drosophila.