Unusual phenotype of intestinal intraepithelial lymphocytes in the rat: predominance of T cell receptor alpha/beta+/CD2- cells and high expression of the RT6 alloantigen.

The phenotype of intraepithelial lymphocytes (IEL) from the small intestine of adult rats was studied by flow cytometry. Using appropriate monoclonal antibodies the expression patterns of the T cell receptor alpha/beta (TcR2), CD2, the alloantigen RT6 and several other T cell antigens were analyzed. The vast majority of rat IEL expressed TcR2 which is in contrast with data reported for the mouse. The comparison of IEL with lymph node cells revealed major phenotypic differences. Whereas CD2 was present on virtually all lymph node T cells it was found on only less than 5% of IEL. The T cell-specific differentiation antigen RT6 present on only a fraction of lymph node cells was found on about 99% of IEL demonstrating uniform expression with an approximately tenfold higher density. Identity of the detected molecule with RT6 was proven by using congenic controls and by the demonstration of phosphatidylinositol linkage to the IEL membrane. About 86% of IEL expressed CD8 but a substantial proportion of these cells co-expressed the CD4 molecule (34%). Two-color analysis revealed that the CD4+CD8+ double-positive subset completely lacked CD45RB suggesting that they represent memory cells. In the CD4-CD8+TcR2+ subset there was a remarkable heterogeneity of CD5 expression. A substantial number of these cells did not express CD5 despite high density of TcR2. Phenotypic peculiarities found on all or most IEL such as the lack of CD2 and the increased expression of RT6 indicate that the intestinal epithelial environment exerts strong effects on the development and maturation of these cells.