TLR4 and infection: Non-catalytic PGRPs function as pathogen pattern recognition receptors and activate the Toll and Imd pathways in Drosophila upon infection, while catalytic PGRPs cleaves peptidoglycan, acting, therefore, as negative regulators of the immune response (by removing peptidoglycan) or as effectors (by killing bacteria) (Palmer and Jiggins, 2015).