NOD2 and bacterial infectious disease: After bacterial infection, NOD2 recognizes muramyl dipeptide (MDP) and then activates NF-κB, thus upregulating the transcription of defensins.193–195 NOD2-mediated defensin regulation is beneficial in protecting against Haemophilus influenzae-induced otitis media.196 In addition, Nod2-deficient mice show different intestinal microbiota compositions from wild-type mice and increased susceptibility to infection upon challenge with Listeria monocytogenes.