The effects and immunologic mechanisms of Helicobacter pylori infection on AOM/DSS induced colitis-associated cancer in mice

Abstract

Objective: To investigate the effects and potential mechanisms of Helicobacter pylori (H.pylori) infection on azoxymethane (AOM)/dextran sulfate sulphate (DSS) induced colitis-associated cancer (CAC) in mice. Methods: A total of 60 specific pathogen free C57BL/6J mice were randomly divided into four groups: normal control group (control group, n=9), H. pylori-infected group (Hp group, n=9), AOM/DSS-treated group (AOM/DSS group,n=21) and AOM/DSS-treated with H.pylori infection group (Hp+AOM/DSS group, n=21). Mice were sacrificed on day19, 45 or 85 after AOM/DSS challenge. Histopathological changes in colonic tissues were determined by hematoxylin and eosin staining. Flow cytometry analysis was performed to determine T helper cells 17 (Th17) and regulatory T cells (Treg) in colonic lamina propria. The expression levels of Th17-and Treg-associated cytokines and transcription factors [interleukin (IL)-10, IL-17A, retinoic acid receptor-related orphan receptor γt (RORγt) and forkhead box P3 (Foxp3)] were determined by quantitative real-time polymerase chain reaction and enzyme-linked immunosorbent assay. Results: There were no histopathological changes in colonic tissues of mice in control group and Hp group. H.pylori colonization reduced the histopathological scores at the stages of colitis (day 19) and dysplasia (day 45), and also decreased tumor load (day 85) in mice treated with AOM/DSS (all P<0.05). Compared with AOM/DSS group, the percentages of CD3(+)CD4(+)IL-17A(+)Th17 and CD3(+)CD4(+)IL-17A(+)Foxp3(+)Treg cells (1.88±0.17 vs 2.07±0.89, 1.06±0.13 vs 1.89±0.23) and the expression levels of RORγt and IL-17A (1.08±0.59 vs 2.35±1.35, 2.96±0.92 vs 7.78±4.57) were decreased in colonic tissues of Hp+AOM/DSS group (all P<0.05). The percentages of CD3(+)CD4(+)CD25(+)Foxp3(+)Treg and CD3(+)CD4(+)IL-10(+)Foxp3(+)Treg cells (20.60±3.39 vs 15.63±2.71, 2.94±0.52 vs 2.14±0.47) and the expression levels of Foxp3 and IL-10 [17.59(13.77,24.87) vs 6.27(4.41,13.36), 3.52(1.59,5.99) vs 1.17(1.15,2.75)] in colonic tissues were higher (all P<0.05) in mice of Hp+AOM/DSS group compared with AOM/DSS group on day 85. Conclusion: H.pylori infection slows the progress from inflammation to tumor in a AOM/DSS induced CAC modal, accompanied with the downregulation of Th17 response and upregulation of Treg response.