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-1beta and TLR4 protein expression; NF-kappaB DNA binding activity assay; as well as IL-1beta, TNFalpha, 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-1beta protein expression; NF-kappaB DNA binding activity; as well as IL-1beta and TNFalpha mRNA expression of the peritoneal macrophages in Nod2(2939iC) mice. Collectively, the increase of bacterial killing activity, IL-1beta expression, and NF-kappaB DNA binding activity of macrophages in Nod2(2939iC) mice suggests that NOD2 is a positive regulator of NF-kappaB/IL-1beta-mediated innate response to bacteria challenge in Crohn's disease.