Interleukin-2 And Platelet Activation In The Pathogenesis Of Ulcerative Colitis

Part One The Study on the Susceptibility of IL2 Heterozygous Mice to DSS Induced ColitisBackground:Interleukin-2 is a cytokine essential to several important T-lymphocyte functions such as proliferation, differentiation and activation. The IL-2 gene has previously been inactivated in mice by homologous recombination and mice homozygous (IL-2-/-) for the IL-2 mutation develop a severe T-cell dependant intestinal inflammation highly reminiscent of human colitis ulcerosa. The heterozygous mice (IL-2+/-) have reduced levels of IL-2 in the intestine, but are nevertheless clinically normal and do not develop an intestinal inflammation. Aims In order to study whether the reduced IL-2 levels predispose the heterozygous mice to colonic inflammation we have exposed both wild type mice (IL-2+/+) and heterozygous IL-2 mice to dextran sulphate sodium (DSS) to induce colitis. Methods:Both IL-2+/- and wild type groups with 12 mice each of age-and sex-matched mice were exposed to 3.5% DSS for 3 or 6 days. Daily evaluation of the progression of colitis was monitored by weighing and examination for rectal bleeding, loose stools and diarrea. Histological analysis was performed using HE staining and inflammation scoring. Specific markers for macrophage, granulocyte, B cell and T cell were used for immunohistochemical and morphometric analysis. Cytokine profile of T cells were detected using qRT-PCR assays. T cell proliferation assay was performed after CD3ε and CD28 stimulations for 24, 48 and 72 hours using β -scintillation counter. Results: The results presented in this study show that the heterozygous mice have a lower susceptibility to DSS induced colitis than the wild type mice. Immunomorphometric analysis revealed that the heterozygous mice fail to upregulate the number of T cells when the inflammation process continues. T cells isolated from the small intestine and colon also display reduced expression rates of cytokines IL-2, IL-4, and IL-10 using qRT-PCR assays and splenic T cells from heterozygous mice proliferate at a lower rate when compared to cells isolated from the wild type mice. Conclusion: These results suggest a defect of the T cells from heterozygous mice to react adequately to the induced colonic inflammation,which might contribute at leastpartially to the lowed susceptibility of IL2 heterozygous mice to DSS induced colitis. IL2 plays an important role on the pathogenesis of ulcerative colitis. Key words: IL2 heterozygous mice, wild type mice, DSS colitis, cytokine expression, qRT-PCR, T cell proliferation...