The multiple functions of the PGRP family in Drosophila immunity

The innate immune system discriminates between infectious non-self and self using germ-line-encoded pattern recognition receptors (PRRs) that are highly conserved from insects to mammals. Peptidoglycan recognition protein (PGRP) is one of the hallmark pattern recognition receptors responsible for detecting unique bacteria-derived peptidoglycans. The PGRP family comprises several members (13 in Drosophila, 7 in Anopheles, and 4 in mammals) and are differentially expressed on immune-responsive organs. Some PGRPs have amidase or bactericidal activities and function as immune modulators, whereas others have lost their enzymatic activity, but still have crucial roles in the activation of innate immune signaling. Evidence from recent Drosophila studies suggests that PGRPs have a role in a variety of immune reactions, such as in the activation of the prophenoloxidase cascade, the production of antimicrobial peptides through the activation of the Toll and Imd pathways, intracellular bacteria recognition, and phagocytosis.