ACTIVATED RAT T-CELLS SYNTHESIZE AND EXPRESS FUNCTIONAL MAJOR HISTOCOMPATIBILITY CLASS-II ANTIGENS

In the present report, we studied the presence and functional signific ance of major histocompatibility complex (MHC) class II antigen on rat T cells. Most rat T-cell lines cultured in vitro were found to be MHC class II+. Also, these T-cell lines were shown to synthesize MHC clas s II molecules. Immunohistochemical and flow cytometric double stainin gs for T-cell receptor (TCR) and MHC class II showed that in vivo as w ell a large proportion of T cells was MHC class II+. The immunohistoch emical staining of spleen sections enabled us to characterize the MHC class II+ and MHC class II- T cells. It was shown that resting T cells in vivo were MHC class II-. In contrast, activated T cells, as determ ined by their localization in the marginal zone of the spleen, proved to be MHC class II+. Finally, T-cell clones were found to be able to p resent peptidic antigens, but could only poorly present more complex e xogenous antigens, probably due to inefficient uptake of such antigens . These features would endow activated rat T cells with the capacity t o present cell-specific self-proteins, such as TCR, to regulatory CD4( +) MHC class II-restricted T cells, as was described by our group else where.