Peptidoglycan recognition proteins (PGRPs).

Innate immune system recognizes microorganisms through a series of pattern recognition receptors that are highly conserved in evolution. Peptidoglycan recognition proteins (PGRPs) are pattern recognition molecules that are conserved from insects to mammals and recognize bacteria and their unique cell wall component, peptidoglycan (PGN). Drosophila, mosquito, and mammals have families of 13, 7, and 4 PGRP genes, respectively, and some of these genes are alternatively spliced. PGRPs are differentially expressed in various cells and tissues, their expression is often upregulated by bacteria, and they mediate host responses to bacterial infections. Insect PGRPs have four known effector functions that are unique for insects: activation of prophenoloxidase cascade, activation of Toll receptor, activation of Imd pathway, and induction of phagocytosis. One function, amidase activity, is shared by some insect and mammalian PGRPs, whereas antibacterial activity of some mammalian PGRPs is unique for mammals.