Cutting Edge: Crohn’s Disease-Associated Nod2 Mutation Limits Production of Proinflammatory Cytokines To Protect the Host from Enterococcus faecalis-Induced Lethality

Nucleotide-binding oligomerization domain 2 (Nod2) mutations including L1007fsinsC are associated with the development of Crohn's disease (CD). These CD-associated Nod2 mutations are common in healthy white populations, suggesting that they may confer some protective function, but experimental evidence is lacking. Using a mouse strain that expresses Nod2(2939iCstop), the equivalent of the L1007fsinsC mutation, we found that macrophages homozygous for Nod2(2939iCstop) are impaired in the recognition of muramyl dipeptide and Enterococcus faecalis, a commensal bacterium that is a common cause of sepsis-associated lethality in humans. Notably, Nod2 deficiency and homozygocity for Nod2(2939iCstop) were associated with reduced production of TNF-α and IL-6 and lethality after systemic infection with E. faecalis despite normal bacteria loads. Consistently, inhibition of TNF-α signaling protected wild-type mice from E. faecalis-induced lethality. These results suggest that the same Nod2 mutation can increase the susceptibility to CD, but also protect the host from systemic infection by a common enteric bacterium.