THYMIC EXPRESSION OF MYELIN BASIC-PROTEIN (MBP) - ACTIVATION OF MBP-SPECIFIC T-CELLS BY THYMIC CELLS IN THE ABSENCE OF EXOGENOUS MBP

Previous studies have shown golli-myelin basic protein (MBP) mRNA to b e expressed in the thymus of normal SJL mice, but translation of the m RNA was not assessed, To test for the presence of immunoreactive prote in, single cell suspensions were prepared from adult SJL thymus and cu ltured with syngeneic MBP-specific T cells. After 48 h [H-3]thymidine was added to the microcultures to assess T cell proliferation. MBP-spe cific T cell lines proliferated strongly (stimulation index range, 13- 31). T cell lines specific for MBP exon 2, MBP peptide 89-101, proteol ipid protein peptide 139-151, and OVA gave stimulation indices of 10-1 3, 5-6, 2-3, and 2-3, respectively. Stimulatory activity could be abro gated by irradiation of either the thymic cells or the MBP-specific T cells. Stimulatory activity was a property of a minor population of pl astic-adherent thymic cells. Monoclonal anti-I-A(s) Ab added to the mi crocultures inhibited the reaction by 77%. MBP-specific T cells cultur ed with syngeneic nonirradiated thymus cells in the absence of added M BP transferred experimental autoimmune encephalomyelitis adoptively to syngeneic recipients. These findings indicate that golli-MBP mRNA is translated in normal SJL thymus, and that peptides reactive with MBP-s pecific T cells in the context of class II MHC molecules are expressed .