Increased presence of effector lymphocytes during Helicobacter hepaticus -induced colitis

AIM: To identify and characterize drosophila mothers against decapentaplegic (SMAD)3-dependent changes in immune cell populations following infection with Helicobacter hepaticus (H. hepaticus). METHODS: SMAD3-/- (n = 19) and colitis-resistant SMAD3+/- (n = 24) mice (8-10 wk of age) were infected with H. hepaticus and changes in immune cell populations [T lymphocytes, natural killer (NK) cells, T regulatory cells] were measured in the spleen and mesenteric lymph nodes (MsLNs) at 0 d, 3 d, 7 d and 28 d post-infection using flow cytometry. Genotype-dependent changes in T lymphocytes and granzyme B+ cells were also assessed after 28 d in proximal colon tissue using immunohistochemistry. RESULTS: As previously observed, SMAD3-/-, but not SMAD3+/- mice, developed colitis, peaking at 4 wk post-infection. No significant changes in T cell subsets were observed in the spleen or in the MsLNs between genotypes at any time point. However, CD4+ and CD8+/CD62Llo cells, an effector T lymphocyte population, as well as NK cells (NKp46/DX5+) were significantly higher in the MsLNs of SMAD3-/- mice at 7 d and 28 d post-infection. In the colon, a higher number of CD3+ cells were present in SMAD3-/- compared to SMAD3+/– mice at baseline, which did not significantly change during infection. However, the number of granzyme B+ cells, a marker of cytolytic lymphocytes, significantly increased in SMAD3-/- mice 28 d post-infection compared to both SMAD3+/- mice and to baseline values. This was consistent with more severe colitis development in these animals. CONCLUSION: Data suggest that defects in SMAD3 signaling increase susceptibility to H. hepaticus-induced colitis through aberrant activation and/or dysregulation of effector lymphocytes.