Using as a model organism an opportunistic pathogen, Helicobacter hepaticus, commonly residing in the lower bowel of mice, we have shown in Rag2-deficient mice (otherwise lacking lymphocytes) that gut microbiota modulate inflammatory bowel disease and inflammation-associated colon cancer, a cancer process inhibited by properly functioning IL-10-dependent TREG (35, 36). Here, IL10 is linked to cancer.