Class II major histocompatibility complex on rat intestinal intraepithelial lymphocytes

Intestinal intraepithelial lymphocytes (IEL) are comprised of unique T cell subsets some of which have unconventional activation requirements and/or responses. Accordingly, we examined the expression of lymphocyte markers and the activation antigen, class II major histocompatibility complex (MHC), on enriched rat IEL by 2- and 3- color flow cytometry. Rat IEL are 70% CD8+ and 33% CD4+ cells; 27% of IEL co-express CD4 and CDS. CD8⁺CD4-aβTCR- IEL account for 9% of cells. We detect a large population (24-73%, mean 39%) of rat IEL that express class II MHC (MRC-OX-8), and have localized its expression to both CD8+ and CD4+ T cells. In samples with a low percentage of class II MHC+ cells (2327%), virtually all class II MHC+ cells are CD8CD4- cells; however, in IEL samples with a high percentage (33-73 %) of class H MHC+ cells, 30% of class II MHC+ cells are CD4+. Patterns of class II MHC expression differ on the two subsets; CDS+ cells express class II MHC at a low intensity and CD4+ cells tend to express class II MHC at a higher intensity. We are further characterizing the CD8+CD4-class II MHC+ cells for TCR (αβ versus γδ) and CD8 molecule (aa versus αβ) phenotypes. Supported by the Crohn's and Colitis Foundation of Canada, and the Natural Sciences and Engineering Research Council of Canada.