Nod2 Mutation Enhances NF-kappaB Activity and Bacterial Killing Activity of Macrophages

NOD2, an intracellular sensor of bacteria, are linked to increased susceptibility to bacteria in Crohn's disease (CD). The NOD2 protein is expressed mainly by macrophages and dendritic cells. This study is to examine the role of NOD2 in the innate response of macrophages to bacterial challenge. First, peritoneal macrophages and alveolar macrophages were harvested from WT, Nod2(2939iC), as well as TLR4(-/-) mice and incubated with E. coli or P. aeruginosa. Bacterial killing activity; IL-1 beta and TLR4 protein expression; NF-kappa B DNA binding activity assay; as well as IL-1 beta, TNF alpha, TLR2, TLR4 and TLR9 mRNA expression of macrophages were examined. We found that alveolar macrophages and peritoneal macrophages of Nod2(2939iC) mice but not WT mice or TLR4(-/-) mice demonstrated a significant increase of E. coli killing activity. Bacterial challenge also induced a significant increase of pro-IL-1 beta protein expression; NF-kappa B DNA binding activity; as well as IL-1 beta and TNF alpha mRNA expression of the peritoneal macrophages in Nod2(2939iC) mice. Collectively, the increase of bacterial killing activity, IL-1 beta expression, and NF-kappa B DNA binding activity of macrophages in Nod2(2939iC) mice suggests that NOD2 is a positive regulator of NF-kappa B/IL-1 beta-mediated innate response to bacteria challenge in Crohn's disease.