IL-10 signaling prevents gluten-dependent intraepithelial CD4+ cytotoxic T lymphocyte infiltration and epithelial damage in the small intestine.

Breach of tolerance to gluten leads to the chronic small intestinal enteropathy celiac disease. A key event in celiac disease development is gluten-dependent infiltration of activated cytotoxic intraepithelial lymphocytes (IELs), which cytolyze epithelial cells causing crypt hyperplasia and villous atrophy. The mechanisms leading to gluten-dependent small intestinal IEL infiltration and activation remain elusive. We have demonstrated that under homeostatic conditions in mice, gluten drives the differentiation of anti-inflammatory T cells producing large amounts of the immunosuppressive cytokine interleukin-10 (IL-10). Here we addressed whether this dominant IL-10 axis prevents gluten-dependent infiltration of activated cytotoxic IEL and subsequent small intestinal enteropathy. We demonstrate that IL-10 regulation prevents gluten-induced cytotoxic inflammatory IEL infiltration. In particular, IL-10 suppresses gluten-induced accumulation of a specialized population of cytotoxic CD4+CD8αα+ IEL (CD4+ CTL) expressing Tbx21, Ifng, and Il21, and a disparate non-cytolytic CD4+CD8α- IEL population expressing Il17a, Il21, and Il10. Concomitantly, IL-10 suppresses gluten-dependent small intestinal epithelial hyperproliferation and upregulation of stress-induced molecules on epithelial cells. Remarkably, frequencies of granzyme B+CD4+CD8α+ IEL are increased in pediatric celiac disease patient biopsies. These findings demonstrate that IL-10 is pivotal to prevent gluten-induced small intestinal inflammation and epithelial damage, and imply that CD4+ CTL are potential new players into these processes.

Colonic tolerance develops in the iliac lymph nodes and can be established independent of CD103(+) dendritic cells.

Tolerance to harmless exogenous antigens is the default immune response in the gastrointestinal tract. Although extensive studies have demonstrated the importance of the mesenteric lymph nodes (MLNs) and intestinal CD103(+) dendritic cells (DCs) in driving small intestinal tolerance to protein antigen, the structural and immunological basis of colonic tolerance remain poorly understood. We show here that the caudal and iliac lymph nodes (ILNs) are inductive sites for distal colonic immune responses and that colonic T cell-mediated tolerance induction to protein antigen is initiated in these draining lymph nodes and not in MLNs. In agreement, colonic tolerance induction was not altered by mesenteric lymphadenectomy. Despite tolerance development, CD103(+)CD11b(+) DCs, which are the major migratory DC population in the MLNs, and the tolerance-related retinoic acid-generating enzyme RALDH2 were virtually absent from the ILNs. Administration of ovalbumin (OVA) to the distal colon did increase the number of CD11c(+)MHCII(hi) migratory CD103(-)CD11b(+) and CD103(+)CD11b(-) DCs in the ILNs. Strikingly, colonic tolerance was intact in Batf3-deficient mice specifically lacking CD103(+)CD11b(-) DCs, suggesting that CD103(-) DCs in the ILNs are sufficient to drive tolerance induction after protein antigen encounter in the distal colon. Altogether, we identify different inductive sites for small intestinal and colonic T-cell responses and reveal that distinct cellular mechanisms are operative to maintain tolerance at these sites.