Murine intestinal intraepithelial lymphocytes (IEL) from unprimed thymus-bearing and athymic nude mice were characterized according to the expression of murine lymphocyte antigenic markers and cytotoxic activity. The majority of IEL from thymus-bearing mice were Lyt-2+, L3T4- lymphocytes, over half of which did not express Thy-1 surface antigens. Nude IEL and spleen cells were void of Thy-1+ cells; however, Lyt-2 antigens were expressed on a significant proportion of IEL, but not splenic lymphocytes. Overall, 40-70% of IEL from either thymus-bearing or athymic mice expressed the cytotoxic activation antigen, CT-1, and the J11d lymphocyte marker, both of which were associated with a population of Thy-1-, Lyt-2+ cytotoxic IEL. These data are taken to mean that the intestinal epithelium is a site uniquely enriched for activated cytotoxic cells, a significant proportion of which originate as non-thymus-derived lymphocytes with acquired lytic activity.

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