Without defense reactions, any organism would perish from the mere growth of harmless microbes, as microbes colonize all living matter. A rapid innate immune system can stop such microbes. Insects rely solely on an innate response as they lack antibodies.
The immune system must first recognize the invading microbe as foreign to start the innate defense. We are studying the nature of the interaction between the microbial signature molecules and their receptors. In insects, receptors that recognize peptidoglycan seem to be of outmost importance for the recognition of bacteria.
We have also found that some members of this family of peptidoglycan recognition proteins (PGRPs) are enzymes cleaving peptidoglycan into pieces that do not stimulate the immune system. Thus proteins belonging to the same family are either positive or negative regulators of innate immunity.