Morphological Changes in the Thymus, Composition of Its Cells, and Subpopulations of Peripheral Blood Lymphocytes during Experimental Acute Ulcerative Colitis

Morphological changes in the thymus and composition of its cells and peripheral blood lymphocytes were studied in experiments on C57Bl/6 mice with sodium dextran sulfate-induced acute ulcerative colitis. Severe acute ulcerative colitis in rats was accompanied by stage III-IV accidental involution of the thymus. This state was characterized by inversion of the layers, death of thymocytes, and increase in the number and area of thymic corpuscles from CK19⁺ epithelial cells. Flow cytofluorometry revealed an increase in the relative number of F4/80⁺ macrophages in the thymus stroma and CD4^—CD8^—CD45⁺CD11c⁺ dendritic cells and CD326⁺UEA⁺CD205^— epithelial cells in the medulla. By contrast, the count of CD326⁺UEA^—CD205⁺ epithelial cells remained unchanged in the cortex. Accidental involution of the thymus was accompanied by an increase in the number of apoptotic AnnV⁺PI^— cells, but decrease in the count of lymphocytes, CD3^—CD19⁺ B lymphocytes, CD3⁺CD8⁺ cytotoxic T lymphocytes, immature CD4⁺CD8⁺ lymphocytes, and CD3⁺CD4⁺ T helpers. The level of peripheral blood endotoxin in adult male C57Bl/6 mice with fibrinous ulcerative colitis was 10-fold lower than in the control. Moreover, we observed a decrease in the absolute number of leukocytes, lymphocytes, CD3⁺CD4⁺ T helpers, CD3⁺CD8⁺ cytotoxic T lymphocytes, CD4⁺CD25⁺FOXP3⁺ regulatory T lymphocytes, and CD3^—CD19⁺ B lymphocytes in the peripheral blood of animals.