Cytokine mRNA expression in intestinal tissue of interleukin-2 deficient mice with bowel inflammation

Background—Mice deficient in interleukin-2 (IL-2) develop inflammatory bowel disease resembling ulcerative colitis in humans. Recent studies provided evidence that αβ T cells, particularly CD4 T cells, rather than B cells, are involved in the pathogenesis of bowel inflammation of IL-2 deficient mice. Aim—To analyse the pattern of expression of cytokine mRNA in intestinal tissue of normal and IL-2 deficient mice. Methods—Expression of β-actin, IL-1α, IL-1β, IL-6, IL-10, tumour necrosis factor α (TNF-α), interferon γ (IFN-γ) and transforming growth factor β1 (TGF-β1) mRNA was analysed in colon and small intestinal tissue of both IL-2 deficient (IL-2−/−) mice and normal (wild type) litter mates (IL-2+/+) at different ages by using qualitative, as well as semiquantitative, competitive reverse transcription polymerase chain reaction (RT-PCR). Results were correlated with the phase of progression of the disease, as determined by histology. Results—IL-2−/− mice had expressed low levels of IL-1α, IL-1β, IL-6, TNF-α, and IFN-γ mRNA in the colon by 1.5 weeks of age. In advance of the development of histologically and clinically detectable bowel inflammation, expression of IL-1α, IL-1β, IL-6, TNF-α, IFN-γ, and IL-10, but not TGF-β1, mRNA increased in the colon of IL-2 deficient mice. In contrast, IL-2+/+ mice expressed TGF-β1 mRNA in colon tissue at 13 and 23 weeks of age, but not IL-1α, IL-1β, IL-6, TNF-α, IL-10, or IFN-γ mRNA. Levels of expression of cytokine mRNA in tissue from the small intestine were comparable in IL-2−/− and IL-2+/+ mice. Conclusions—Bowel inflammation in IL-2 deficient mice is preceded by an increase in IL-1α, IL-1β, TNF-α, and IFN-γ mRNA expression in colon tissue. Low levels of TGF-β1, but high levels of IL-1α, IL-1β, IL-6, TNF-α, IFN-γ, and IL-10 mRNA expression correlate with the manifestation of severe colitis, and suggest that T cells and macrophages are involved in bowel inflammation of IL-2 deficient mice.