CD4+ CD8+ murine intestinal intraepithelial Iymphocytes

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Abstract
We have studied a population of CD4+ intestinal intraepithellal Iymphocytes using two-color flow cytometrlc analyses, and in highly purified fluorescent-activated cell-sorted preparations. Although CD4+ T cells present within the epithelial immune compartment comprised only ∼10–20% of the total intestinal epithelial lymphoid cells, an unusually high proportion of those CD4+ lymphocytes expressed a CD4+CD8+ phenotype which is rarely encountered in peripheral T cells. By comparison, CD4+ lymphocytes from spleen or lymph nodes existed exclusively as single-positive T cells. Analyses of CD4 and CD8 expression on lymphocytes from Peyer's patches, the lamina propria, and IEL indicated that CD4+CD8+ lymphocytes were unique to the IEL. Using CD4+CD8+ preparations obtained by fluorescent-activated cell sorting, CD4+CD8+ epithelial T cells were found also to express CD3 and Thy-1 surface markers. This heretofore undescribed extrathymic population of double-positive T cells constitutes a unique peripheral T cell subset which may be involved in intestinal T cell maturation and development, or could represent a highly specialized effector population.