IL-10 signaling has also been associated with the pathogenesis of human IBD. IL-10 can regulate Z-VAD-FMK Caspase excessive proinflammatory cytokine production by lamina propria mononuclear cells isolated from IBD patients (22). PBMCs from CD patients homozygous for NOD2 mutations produce lower levels of IL-10 compared with WT cells from healthy volunteers (23, 24), and low mucosal levels of IL-10 in CD patients are associated with severe disease (25). The importance of IL-10 in IBD has recently been highlighted by genome-wide association studies identifying IL-10 as a susceptibility gene for UC and CD (13, 26) and the identification of mutations in the IL-10R gene, resulting in the abrogation of IL-10 signaling, which associate with early onset enterocolitis (27).

Apart from mutations in the IL-10R gene, IL-10�Cdeficient signaling similar to IL-10?/? and STAT3?/? mice is not generally observed in IBD patients, although the clinical evidence described above suggests that, in subpopulations of patients, alterations in IL-10 signaling is a factor that contributes to the pathogenesis of IBD. TLRs have been shown to affect the development of colitis in IL-10?/? mice (28�C30) and chemically induced colitis models (31�C33). However, the contribution of intracellular pathogen PRR, such as NOD2, toward the development of colitis in IL-10?/? mice has not been reported. Whereas genetic association in humans has implicated NOD2 as a key player in the pathogenesis of IBD, NOD2 signaling in mice is not essential for gut homeostasis as mice deficient in NOD2 do not develop spontaneous colitis or differ from WT mice in the development of acute and chronic dextran sulfate sodium (DSS)�Cinduced colitis (4, 34).

However, other studies investigating the role of NOD2 in intestinal inflammation have demonstrated that deletion of NOD2 can impact both positively and negatively on the development of colitis depending on the model system used. For example, MDP administration has been shown to protect mice from 2,4,6-trinitrobenzenesulfonic acid (TNBS) and DSS-induced colitis; the protective role of NOD2 signaling was confirmed as MDP-mediated protection with loss in NOD2?/? mice (35). In contrast, others have demonstrated that NOD2?/? T cells result in reduced chronic colitis following transfer into immunocompromised mice, suggesting that, in the context of T cell�Cmediated colitis, NOD2 signaling can exacerbate inflammation (36).

In this present study, we use the IL-10?/? mouse model of colitis and demonstrate that mice double deficient in IL-10 and NOD2 are protected from developing severe chronic colitis. Both innate and adaptive immune responses contribute to colitis in IL-10?/? mice. Thus, to elucidate the mechanism by which mice are protected, we investigated T cell and macrophage function and demonstrate Drug_discovery that loss of NOD2 signaling in IL-10?/? mice predominantly affects macrophage activity.