Ro/SSA inhibits the autologous mixed lymphocyte reaction.

To test the hypothesis that the Ro/SSA autoantigen can be recognized as antigenic by the human immune system, lymphocytes obtained from normal volunteers were used in in vitro assays evaluating the ability of Ro/SSA (mol. wt 60 kD) to induce B and/or T cell responses. Bovine Ro/SSA strongly inhibited the autologous mixed lymphocyte reaction in a dose-dependent manner without similar effects on concurrently performed allogeneic mixed lymphocyte reactions or T cell proliferation induced by phytohaemagglutinin. Using three colour FACS analysis, Ro/SSA was found to decrease the percentage of CD4+CD45+RA+ T cells in the proliferative, S+(G2+M), phase of the cell cycle. Associated with the decrease in the percentage of suppressor-inducer cells, was the finding that Ro/SSA was able to augment RF production in pokeweed mitogen stimulated cultures of peripheral blood lymphocytes.