The best-studied family of PRRs in humans are the Toll-like receptors (TLRs) [4] , however, the importance of other PRRs including the nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs) [5, 6] , and the retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs) is becoming evident [7, 8] .