Phenotypic heterogeneity of intraepithelial T lymphocytes from mouse small intestine

We have used two-colour flow cytometry to examine the heterogeneity of intraepithelial lymphocytes (IEL) from mouse small intestine. We have confirmed the predominance of CD3+ Thy 1- CD8+ IEL and show that a substantial but variable proportion of CD8+ IEL does not express the alpha beta T-cell receptor (TcR) for antigen. Simultaneous analysis of the co-expression of the alpha and beta chains of the CD8 heterodimer and of the alpha beta TcR revealed three populations of CD8+IEL. The first of these expressed both CD8 alpha and beta chains and had normal expression of V beta families and so represented conventional CD8+ alpha beta TcR+ T cells. The second population comprised alpha beta TcR- T cells (presumed gamma delta TcR+) which expressed only the alpha chain of the CD8 molecule. Finally, we identified a second, unique population of alpha beta TcR+ CD8+ IEL which were also CD8 beta-. Gamma delta + IEL predominated in mice aged less than 8 weeks, but there was a rapid increase in both populations of alpha beta TcR+ CD8+ IEL in older mice. CD8+ IEL were similar to peripheral CD8+ T cells in having high expression of the CD45RB molecule, but CD4+ IEL had generally lower expression of CD45RB than their peripheral counterparts, despite having normal expression of TcR. These findings emphasize the heterogeneity of IEL and underline the need to study phenotypically defined populations.