NOD-like receptors (NLRs): bona fide intracellular microbial sensors

The nucleotide-binding oligomerization domain (NOD)-like receptor (NLR) (nucleotide-binding domain leucine-rich repeat containing) family of proteins has been demonstrated to function as regulators of innate immune response against microbial pathogens. Stimulation of NOD1 and NOD2, two prototypic NLRs, results in the activation of MAPK and NF-κB. On the other hand, a different set of NLRs induces caspase-1 activation through the assembly of an inflammasome. This review discusses recent findings regarding the signaling pathways utilized by NLR proteins in the control of caspase-1 and NF-κB activation, as well as the nonredundant role of NLRs in pathogen clearance. The review also covers advances regarding the cellular localization of these proteins and the implications this may have on pathogen sensing and signal transduction.