No abstract

LC and CC patients have differences in mucosal lymphocyte subsets, with increased proportions of Ki67(+) and CD45RO(+) CD8(+) and CD4(+)8(+) mucosal T cells.

Summary Gαi2‐deficient mice, which spontaneously develop colitis, have previously been reported to have an increased frequency of mature, single positive thymocytes compared to wild‐type mice. In this study we further characterized the intrathymic changes in these mice before and during overt colitis. Even before the onset of colitis, Gαi2–/– thymi weighed less and contained fewer thymocytes, and this was exacerbated with colitis development. Whereas precolitic Gαi2–/– mice had unchanged thymocyte density compared to Gαi2+/– mice of the same age, this was significantly decreased in mice with colitis. Thymic atrophy in Gαi2–/– mice involved mainly the cortex. Using a five‐stage phenotypic characterization of thymocyte maturation based on expression of CD4, CD8, TCRαβ, CD69 and CD62L, we found that both precolitic and colitic Gαi2–/– mice had significantly increased frequencies of mature single‐positive CD4+ and CD8+ medullary thymocytes, and significantly reduced frequencies and total numbers of immature CD4+ CD8+ double‐positive thymocytes compared to Gαi2+/– mice. Furthermore, cortical and transitional precolitic Gαi2–/– thymocytes showed significantly reduced chemotactic migration towards CXCL12, and a trend towards reduced migration to CCL25, compared to wild‐type thymocytes, a feature even more pronounced in colitic mice. This impaired chemotactic migration of Gαi2–/– thymocytes could not be reversed by increased chemokine concentrations. Gαi2–/– thymocytes also showed reduced expression of the CCL25 receptor CCR9, but not CXCR4, the receptor, for CXCL12. Finally, wild‐type colonic lamina propria lymphocytes migrated in response to CXCL12, but not CCL25 and, as with thymocytes, the chemokine responsiveness was significantly reduced in Gαi2–/– mucosal lymphocytes.

One of the most widely used animal models for inflammatory bowel disease (IBD) is the dextran sulfate sodium (DSS)‐induced colitis. We have previously reported that 5 days administration of DSS in C57Bl/6J mice induces a colonic inflammation that progresses into chronicity after DSS removal, whereas in BALB/cJ mice the inflammation resolves within 4 weeks post‐DSS. Here we show that both thymic size and thymocyte numbers dramatically decreased in the acute phase of inflammation in C57Bl/6 mice, 7 days after DSS withdrawal. Mature, CD4+ and CD8+ single positive (SP) CD69lo CD62Lhi thymocytes were enriched in these mice, accompanied by a major decrease in the number of immature double positive (DP) thymocytes. However, the different maturation stages within the DP thymocyte subset were unchanged between healthy and inflamed C57Bl/6J mice. Interestingly, as the inflammation progressed into the chronic phase, the thymus recovered and 2 weeks after the acute inflammatory phase all the thymic parameters investigated in this study were restored to normal. In contrast, BALB/cJ mice only develop mild thymic alterations. Nevertheless, we found that within the double negative (DN) thymocytes an increased frequency and also total numbers of CD44+ CD25− (DN1) cells correlated with the severety of colitis, and that the frequency of CD44− CD25− (DN4) thymocytes decreased proportionally in the acute phase in BALB/cJ mice. Our observations suggest that the thymic effects are intimately connected to the intestinal inflammatory response in colitis regardless of the inflammatory stimuli.

Summary Inflammatory bowel disease (IBD) is associated with imbalances of the local intestinal immune responses, with dysregulated CD4+ T cells contributing to the chronic inflammation. Having demonstrated altered T cell maturation in the thymus in two different mouse models of colitis, we set out to investigate whether abnormalities in T cell maturation is present in patients with ulcerative colitis (UC) or Crohn's disease (CD). Specimens were obtained from peripheral blood (CD; n = 14, UC; n = 22), colon and small intestinal specimens (CD; n = 6, UC; n = 13). As controls, peripheral blood specimens were obtained from healthy volunteers, patients with adenocarcinomas (n = 18) and colonic specimens from patients with adenocarcinomas (n = 14). Recent thymic emigrants were estimated by analysis of the normalized ratio of T cell receptor excision circles (TRECs) by real-time polymerase chain reaction (PCR). The frequency of naive-and proliferating T lymphocytes and markers of extrathymic T cell maturation in the mucosa was analyzed by flow cytometry and real time-PCR. TREC levels in peripheral blood T lymphocytes were similar between IBD patients and controls. In contrast, UC patients demonstrated significantly increased levels of TRECs both in intraepithelial and lamina propria lymphocytes from the colonic mucosa compared to patients with adenocarcinomas and CD. However, markers for extrathymic T cell maturation in the mucosa were not different between controls and IBD patients. The increased TREC levels in mucosal but not peripheral blood lymphocytes in UC patients in the absence of increased extrathymic maturation in situ in the mucosa together demonstrate that recent thymic emigrants are recruited rapidly to the inflamed mucosa of these patients.