Recognition of infectious non-self and activation of immune responses by peptidoglycan recognition protein (PGRP)-family members in Drosophila

Activation of the innate immune response involves recognition of the infectious non-self and subsequent activation of cellular and humoral reactions. Insect humoral reactions depend on primary and secondary responses. The primary response is mediated by the activation of cascades of constitutive proteins present in the hemolymph, such as the prophenoloxidase (proPO) cascade. The secondary response requires transcriptional activation of defense proteins, such as the induction of antimicrobial peptides. Drosophila possess specific mechanisms to discriminate between microbes and respond to infection by inducing the appropriate reactions. In innate immunity, pathogen-associated molecular patterns are recognized. The mechanisms for microbial recognition in Drosophila, however, are largely unknown. Recent data suggest that, in insect immunity, diverse peptidoglycan recognition protein members are involved in distinguishing between invading bacteria and activation of appropriate immune reactions.