T_Reg cells, more than a suppression problem

Chronic intestinal inflammation is associated with the development of colorectal cancer. Regulatory T (T_Reg) cells suppress inflammatory responses and maintain intestinal homeostasis, and therefore they might mitigate the formation of inflammation-associated tumours. Surprisingly, Geis et al. have found that in mice colonized with enterotoxigenic Bacteroides fragilis (ETBF) — a human colonic bacterium associated with inflammatory intestinal diseases — T_Reg cells produce interleukin-17, which promotes the earliest stages of colon carcinogenesis. Depletion of T_Reg cells in ETBF-colonized mice enhanced colitis but diminished tumorigenesis.