The development of Th17 responses towards gut antigens during colitis requires both intestinal inflammation and TLR2/6 stimulation

Interest in T helper cells during the initiation and progression of intestinal inflammation has increased as a result of the probable role of Th17 cells in IBD pathogenesis. The dextran sodium sulfate (DSS) model of colitis recruits many T lymphocytes to the inflamed colon, however, very little is known about the subtype (Th1, Th2, Th17 and Treg) and what factors steer their development. Research on gut antigen-primed T cells in DSS colitis is hampered by a lack of knowledge about the antigens presented in the gut. Thus, an oral tracker antigen (ovalbumin) was employed to follow gut antigenprimed T cells in mice under the influence of gastrointestinal Toll-like receptor (TLR) triggering during DSS-induced colitis. DSS-colitis was induced by administering DSS (1.5%) in the drink water over a period of 6 days. Ovalbumin and the TLR ligands were given orally during the DSS treatment. Ovalbumin-specific CD4+ T cells were detected in the spleens and mesenteric lymph nodes of mice after the resolution of inflammation (14 days after the start of DSS administration). These responses were found in mice that were treated orally with bacteria or with ligands for the TLR2/6 heterodimer during colitis and not in mice that were treated orally with ligands for TLR1/2 and TLR4. Using flow cytometry, it was determined that the ovalbumin-specific CD4+ T cells were Th17 or Treg, expressing either RORγT or Foxp3 respectively. These results demonstrate that breaking tolerance against gut antigens requires a combination of local inflammatory signals to develop gut antigen-specific Th17 and Treg cells that may be found systemically after the resolution of inflammation. These insights will ultimately help elucidate how the gut environment and pathogen-associated molecular patterns steer the development of adaptive immune responses during colitis and how pathogenrecognition receptors can be used to manipulate the development or resolution of inflammation to treat gastrointestinal disease.