Inflammatory bowel disease (IBD) increases the risk of colitis-associated cancer (CAC). Evidences suggest that Helicobacter pylori (H. pylori) infection is associated with a low risk of IBD and protects against experimental colitis in mouse models. However, the effect of H. pylori infection in CAC remains unclear. We previously reported that H. pylori infection increased M2 macrophages in dextran sodium sulfate (DSS)-induced chronic colitis. Tumor-associated macrophages (TAMs) play a pivotal role in colon cancer. Therefore, we established a H. pylori-infected CAC mouse model induced by azoxymethane and DSS to explore the effect of H. pylori infection on TAMs in CAC. Here, we demonstrated that H. pylori infection attenuated the development of CAC by decreasing tumor multiplicity, tumor size, tumor grade and colitis scores. Moreover, H. pylori infection reduced the infiltration of TAMs, particularly M2-like TAMs in CAC tumors, accompanied with the down-regulated pro-inflammatory and pro-tumorigenic factors TNF-α, IL-1β, IL-6 and IL-23 in tumors of CAC mice. Our study suggests that H. pylori infection can reduce TAMs infiltration and regulate cytokines expression in CAC.

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