The immune response to infection can involve up to 2,423 genes, or 13.7% of the genome. Although the fly's transcriptional response to microbial challenge is highly specific to individual pathogens, "Drosophila" differentially expresses a core group of 252 genes upon infection with most bacteria. This core group of genes is associated with gene ontology categories such as antimicrobial response, stress response, secretion, neuron-like, reproduction, and metabolism among others. "Drosophila" also possesses several immune mechanisms to both shape the microbiota and prevent excessive immune responses upon detection of microbial stimuli. For instance, secreted PGRPs with amidase activity scavenge and degrade immunostimulatory DAP-type PGN in order to block Imd activation.