Drosophila Innate Immunity

Abstract Drosophila melanogaster is a useful model for studying innate immunity that has been used to identify and characterise the role of the Toll pathway and nuclear factor‐κB (NFκB) signalling in both insects and mammals. When flies encounter a pathogen, two pattern recognition pathways, Toll and imd, induce a humoral immune response consisting primarily of antimicrobial peptide production. Drosophila also has a cellular immune response in which phagocytic cells engulf and destroy foreign invaders; a melanisation response that generates reactive oxygen species; and an antiviral RNAi ( ribonucleic acid interference) response. Application of Drosophila model has already taught us much about innate immunity. As we expand our research to take a more comprehensive look at how a host responds to infection and what determines the outcome of that infection we can continue to learn more about this complex system from the simple fruitfly. Key Concepts: Drosophila can be used as a model system to study the innate immune system. The Drosophila immunity consists of humoral, cellular and melanisation responses. The humoral immune response involves antimicrobial peptide production, which is induced by the recognition of pathogen‐associated molecular patterns (PAMPs) by patter recognition receptors (PRRs). Two NFκB signalling pathways, Toll and imd, regulate the AMP response to fungal, bacterial and viral pathogens. The cellular immune response is enacted by phagocytic cells known as hemocytes. The melanisation response encapsulates foreign invaders with melanin and produces reactive oxygen species to kill microbes. The fly also has barrier epithelia, native intestinal flora and an RNAi antiviral response which contribute to innate immunity. Physiological and environmental factors can affect the outcome of an infection, including sleep and additional immune challenges. The susceptibility of a fruitfly to bacterial infection depends both on its ability to resist a pathogenic infection and prevent bacterial growth and also its ability to tolerate the bacteria and the consequences of its own immune response.