Impaired Mitogenic Response of Peripheral Blood T Cells in Ulcerative Colitis Is Not Due to Apoptosis

An abnormal immune response may play apathogenic role in ulcerative colitis (UC). Animalmodels suggest that T-cell regulation may be of centralimportance in the inflammatory process. Our aims werethe characterization of the phenotype andfunctional status of circulating T-cells in ulcerativecolitis patients and to determine if activation-inducedcell death in CD4⁺ and CD8⁺lymphocytes in patients differs from healthy controls.Forty-eight patients (24 women and 24 men) fulfillingthe histopathological, clinical, and immunologicalcriteria for UC were studied. T-cell phenotype andfunction were studied in blood lymphocytes from patientswith ulcerative colitis and healthy donors by flowcytometric analysis, as well as ³H]thymidineincorporation. There were no significant differences in the percentage of T-cell subpopulations(CD3, CD4, CD8) and NK cells in the different groups.The percentage of cells in growth phase S+G₂Mat two and three days of phytohemagglutinin (PHA) stimulation was significantly decreased in UCpatients, but the percentage of CD4⁺ andCD8⁺ cells in UC patients that showedapoptosis was not significantly different than that inthe control group. Proliferative responses to IL-4 also suggested that a reducedresponsiveness to this cytokine may be involved in UC.In conclusion, the impaired proliferative response toPHA of T lymphocytes from UC patients is not associated with an in vitro increase in theapoptotic response in CD4⁺ or CD8⁺cells. A reduced IL-4 response may be involved in thispeculiar mitogenic response. These changes may be pathogenic or a favorable adaptivemechanism.