A new antigenic determinant on intra-epithelial lymphocytes and its association with CD45

Rat monoclonal antibodies were prepared against intra-epithelial lymphocytes (IEL) isolated from the gut of Balb/c mice and screened for selective reactivity with mucosal lymphocytes. One antibody, M371, identified a new surface antigen on 30-40% of IEL. It bound to very few, if any, lymphocytes within the lamina propria and to none in other lymphoid tissues; neither did it stain lymph node lymphocytes that had been stimulated in culture with mitogens or alloantigens. The data suggest that M371 identifies a sessile population of IEL and that expression of the antigen is induced locally in the epithelium. In addition to IEL, M371 bound to some goblet cells in the mid and distal small gut but not in the proximal region. Double-staining experiments showed that M371 was highly specific for IEL with the phenotype Lyt-2+, Lyt-3-, Thy-1-, CD3+ and stained a majority of cells in this subpopulation. M371 precipitated a surface molecule approximately 275,000 MW in size, which was also precipitated by antibodies to CD45. Treatment of fixed IEL with sodium periodate prevented staining by M371, suggesting involvement of carbohydrate in the epitope. The specificity of M371 was shown to differ from that of the antibodies CT1 and CT2, which identify a carbohydrate determinant of CD45 expressed on cytotoxic lymphocytes and IEL. The possibility that the gut epithelium provides an environment for the functional differentiation of thymus-independent mucosal T cells is discussed.