Helicobacter hepaticus-induced colitis in interleukin-10-deficient mice: Cytokine requirements for the induction and maintenance of intestinal inflammation

We have previously shown that specific-pathogen-free interleukin-10 (IL-10) -deficient (IL-10 KO) mice reconstituted with Helicobacter hepaticus develo p severe colitis associated with a Th1-type cytokine response. In the prese nt study, we formally demonstrate that IL-12 is crucial for disease inducti on, because mice deficient for both IL-10 and IL-12 p40 show no intestinal pathology following H, hepaticus infection. By using monoclonal antibodies (MAbs) to IL-12, gamma interferon (IFN-gamma), and tumor necrosis factor al pha (TNF-alpha), we have further analyzed the role of these cytokines in th e maintenance of the Th1 response and inflammation in IL-10 KO mice with es tablished H. hepaticus-induced colitis. Treatment of infected colitic IL-10 KO mice with anti-IL-12 p40 resulted in markedly reduced intestinal inflam mation, colonic IFN-gamma, TNF-alpha, and inducible nitric oxide synthase ( iNOS) mRNA levels, and H, hepaticus-specific IFN-gamma secretion by mesente ric lymph node (MLN) cells compared to the findings in control MAb-treated mice. Moreover, the diminished pathology was associated with decreased numb ers of colonic CD3(+) T cells and significantly reduced frequencies of Heli cobacter-reactive CD4(+) Th1 cells in MLN, In contrast, anti-IFN-gamma and/ or anti-TNF-alpha had no effect on intestinal inflammation in IL-IO KO mice with established colitis, Using IL-10/IFN-gamma double-deficient mice, we further show that IFN-gamma is not required for the development of colitis following H, hepaticus infection. MLN cells from infected IL-10/IFN-gamma K O animals secreted elevated amounts of IL-12 and TNF-alpha following bacter ial antigen stimulation, indicating alternative pathways of disease inducti on. Taken together, our results demonstrate a crucial role for IL-12 in bot h inducing and sustaining intestinal inflammation through recruitment and m aintenance of a pool of pathogenic Th1 cells.