Functional heterogeneity of murine intestinal intraepithelial lymphocytes: studies using TCR-αβ⁺ IEL lines and fresh iel isolates reveal multiple cytotoxic subsets differentiated by CD5, CD8α/α, and CD8α/β expression

Three T-cell lines, isolated from murine small intestine epithelia, have been studied with respect to phenotypic properties and cytotoxic activity. All lines were TCR-αβ⁺, Thy-1⁺, CD3⁺, CD4^-, CD⁸⁺ but differed in that one line was CD8α/α⁺, CD5^-; one line was CD8α/α⁺, CD5⁺; and one line was CD8α/β⁺, CD5⁺. Both the CD8α/α⁺, CD5^-, and the CD8α/β⁺, CD5⁺ lines lysed antigen-bearing target cells; however, the latter line also spontaneously lysed natural killer (NK)-sensitive target cells. The CD8α/α⁺, CD5⁺ IEL line was nonlytic for antigen-bearing target cells, for NK-sensitive target cells, and in assays that detect lytic activity regardless of specificity. Three-color flow cytometric analyses of intestinal intraepithelial lymphocytes (IEL) in freshly-extracted preparations indicated that cells with the phenotypes of the three IEL lines are normally present in the murine intestine epithelium, and revealed considerable variability in the distribution and density of CD5 expression on murine IEL. In freshly extracted IEL depleted of CD5 or CD8β by cell sorting, cytotoxicity was found to reside both within the CD5⁺ and the CD5^- IEL subsets, as well as in the CD8β-depleted (i.e., CD8α/α⁺) subset. These findings demonstrate: that cytotoxicity of murine IEL resides among multiple phenotypic subsets; that the distribution and density of CD5 on IEL is more complex than previously described; and that T-cell lines of IEL origin are valuable for dissecting functional properties of specific IEL subsets, particularly those that constitute a small proportion of the total IEL.