Innate Immunity Pathways
Drosophila melanogaster is commonly known as the common fruit fly or vinegar fly. Wild type fruit flies have brick red eyes, are yellow-brown in color, and have transverse black rings across their abdomen. They exhibit sexual dimorphism.
Due to it's small size, ease of culture and short generation time, geneticists have been using Drosophila. It is one of the few organisms whose entire genome is known and many genes have been identified.
Drosophila only have innate immunity and lack an adaptive immune response. The D.melanogaster immune system can be divided into two responses: humoral and cell-mediated. The former is a systemic response mediated through the Toll and IMD pathways, which are parallel systems for detecting microbes. The Toll pathway in Drosophila is known as the homologue of Toll-Like pathways in mammals. Spatzle, a known ligand for the Toll pathway in flies, is produced in response to Gram+ve bacteria, parasites, and fungal infection. Upon infection, pro-Spatzle will be cleaved by protease SPE (Spatzle processing enzyme) to become active Spatzle, which then binds to the Toll receptor located on the cell surface (Fat body, hemocytes) and dimerise for activation of downstream NFkB signaling pathways. On the other hand, the imd pathway is triggered by Gram-ve bacteria through soluble and surface receptors (PGRP-LE and LC respectively).D.melanogaster have a "fat body", which the primary secretory organ and produces AMP's. These peptides are secreted into the haemoplymph and bind infectious bacteria, killing them by forming pores in their cell walls. Other than the fat body, hemocytes,the blood cells in drosophila, are known as the homologue of mammalian monocyte/macrophages, possessing a significant role in immune responses.
Immunity genes list obtained from:
Genome-wide analysis of the Drosophila melanogaster immune response by using oligonucleotide microarrays.
De Gregorio E, Spellman PT, Rubin GM, Lemaitre B.
Proc Natl Acad Sci U S A. 2001 Oct 23;98(22):12590-5. Epub 2001 Oct 16.