Role of Ia antigens in the human autologous mixed lymphocyte reaction.

The role of Ia antigens in the human autologous mixed lymphocyte reaction (MLR) was analyzed. To do this, different mononuclear cell populations were fractionated according to their Ia antigen expression and used as stimulating cells in autologous MLR. Also examined was the effect of two hybridoma monoclonal antibodies specific for human Ia molecules on the autologous MLR. The results show that the stimulating capacity of peripheral blood mononuclear cells is restricted to Ia-bearing cells. While peripheral blood T cells are unable to function as stimulating cells, highly purified Ia+ mixed lymphocyte culture-activated T cells are very effective. The possibility that Ia molecules are directly involved in the autologous MLR is further substantiated by the strong inhibitory effect of monoclonal anti-Ia antibodies.