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.