Class II antigens on canine T lymphocytes

A panel of crossreactive anti‐human, ‐mouse and ‐rat MHC class II monoclonal antibodies (Mabs) was used to examine MHC class II antigen expression on canine T lymphocytes by cytofluorometry. The presence of MHC class II antigens was demonstrated on activated T lymphoblasts as well as on non‐stimulated peripheral blood T lymphocytes. A number of anti‐MHC class II Mabs reacted only with activated T lymphoblasts. Immunoprecipitation studies confirmed the Ia‐like or MHC class II molecular character of the antigens on canine T cells. The expression of MHC class II antigens on peripheral blood T lymphocytes appeared to be not induced by stimulation of the T cells, as purified T lymphocytes of specific pathogen free dogs reacted with anti‐MHC class II Mabs. Moreover, the study indicates that MHC class II antigen expression is present in the neonatal thymus. Lectin stimulated and allogeneically stimulated T lymphoblasts showed a stronger expression of MHC class II antigens in comparison with non‐stimulated T cells.