Over‐expression of interleukin 10 in mucosal T cells of patients with active ulcerative colitis

SUMMARY Ulcerative colitis (UC), a chronic inflammatory bowel disease, exhibits pronounced increase of T lymphocytes in the inflamed mucosa. To understand the role of intestinal T lymphocytes in the pathogenesis of UC their cytokine production in the mucosa was analysed. Intestinal T lymphocytes of UC, Crohn's disease and control patients were analysed for cytokine mRNA levels by real‐time quantitative reverse transcription‐polymerase chain reaction (RT‐PCR) directly after isolation without in vitro stimulation. Frequencies of cytokine positive cells were determined in UC and control colon by immunomorphometry. T lymphocytes in normal colon expressed interleukin (IL)‐2, interferon (IFN)‐γ, tumour necrosis factor (TNF)‐α and transforming growth factor (TGF)‐β1, but not IL‐4, IL‐5 or IL‐10. In UC, a highly significant increase in IL‐10 mRNA levels in T lymphocytes and an increased frequency of IL‐10 positive cells was seen in colon. IL‐10 mRNA levels were also elevated in T lymphocytes of the non‐inflamed ileum and correlated with disease activity at both locations. CD4+ T lymphocytes were the major source of IL‐10 mRNA. IL‐2, IFN‐γ and TNF‐α mRNA levels were decreased in colonic T lymphocytes, and virtually no IL‐2, IFN‐γ, TNF‐α or TGF‐β positive cells were detected in basal lymphoid aggregates. However, scattered IL‐10 positive cells were found here. Lamina propria outside the aggregates contained IL‐10‐, IFN‐γ, TNF‐α and TGF‐β but not IL‐2 positive cells. T cells of UC patients did not express IL‐4 or IL‐5. Taken, together the data suggest a generalized activation of IL‐10 producing CD4+ T cells along the intestine of UC patients. The local environment seems to determine the biological consequences of elevated IL‐10.