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[Presence of thymus-dependent CD4+8+ intestinal intraepithelial lymphocytes and their characteristics in mice].

The purpose of this study was the investigation of the T cell subsets in the gut-associated lymphoid tissues. CD4+8+ T cells were found to appear temporarily in Peyer's patches of mice at 2 to 3 weeks after birth. They disappeared within a short period of time from Peyer's patches, but constantly populated in the intestinal intraepithelial lymphocytes (iIEL). Three to 10% of iIEL were CD4+8+ in the specific pathogen-free (SPF) condition throughout life. They are mature T cells with a high density of CD3 and TcR alpha beta and found to respond to immobilized anti-CD3 antibody. The appearance of CD4+8+ T cells in iIEL was found to be dependent on the thymic selection, since they were absent in the athymic nu/nu mice, and the V beta gene usage was dictated by the pattern of thymic selection. CD4+8+ T cells were not found in the germ-free mice but increased in the SPF old mice. These results indicate that the iIEL contain a unique subset of thymus-derived mature CD4+8+ T cells. These cells may repopulate after the thymic selection in the intestine and increase in response to the intestinal microenvironments.