NLRs join TLRs as innate sensors of pathogens.

Pathogen-recognition receptors (PRRs) are key components of immune systems and are involved in innate effector mechanisms and activation of adaptive immunity. Since their discovery in vertebrates, Toll-like receptors (TLRs) have become the focus of extensive research that has revealed their significance in the regulation of many facets of our immune system. What makes TLRs so central and fascinating is their ability to recognize microbes and directly initiate specific signal transduction cascades that alert the host defences. In this review, we discuss the function and biology of a new family of PRRs, the NACHT-LRRs (NLRs), which include both nucleotide-binding oligomerization domains (NODs) and NALPs [NACHT-, LRR- and pyrin domain (PYD)-containing proteins], and underline some intriguing similarities between NLRs and TLRs that emphasize the role of NLRs as a complementary system for host-microbe interactions.