Abstract Highly purified populations of human peripheral blood macrophages, null, B, and T lymphocytes, and mixed populations of B plus null cells were compared for their ability to act as stimulators in the autologous and allogeneic mixed leukocyte reaction (MLR), examined for susceptibility of stimulatory capabilities to inhibition by in vitro corticosteroids, and studied with regard to the ability of the different cell types to generate suppressor cells. By using a sequence of G-10, anti-human F(ab’)2-G-200, and E rosette techniques, isolated populations of cells were obtained and 50,000 responder T cells were placed in culture for 6 days with 200,000 irradiated (4000 R) stimulator cells. Macrophages (monocytes) or mixed populations of B plus null cells were potent stimulators of autologous T cells and isolated null cells were intermediate in capability, whereas highly purified B cells and T cells did not stimulate at all. In contrast, B cells as well as macrophages, null cells, and mixed populations of B plus null cells were all potent stimulators of allogeneic T cells. The ability of a highly purified population of B cells to stimulate allogeneic but not autologous T cells indicates that the antigens that stimulate in autologous MLR may be distinct from LD antigens. Preincubation in vitro for one hour with hydrocortisone (10−4 M to 10−8 M) had no effect on either autologous or allogeneic MLR if either responder T cells or stimulator B plus null cells were treated. However, preincubation of macrophage stimulators with hydrocortisone resulted in complete inhibition of both autologous and allogeneic MLR. Thus, monocyte-mediated stimulation of both autologous and allogeneic MLR is markedly susceptible to the effects of corticosteroids. Finally, either macrophage or null cell stimulation of autologous T cells caused generation of suppressor cells capable of suppressing both subsequent autologous and allogeneic MLR, demonstrating that the major stimulating cell types in autologous MLR also generate suppressor cells. These studies demonstrate that the cell surface antigens that stimulate in the autologous as opposed to the allogeneic MLR may be distinct and separate with regard to identity, and heterogeneous with regard to distribution. Furthermore, the macrophage not only is a potent stimulator cell type in the autologous MLR but also generates suppressor cells during the reaction and is markedly sensitive to corticosteroid inhibition.

MacDermott, R. P., & Stacey, M. C. (1981). Further characterization of the human autologous mixed leukocyte reaction (MLR). The Journal of Immunology, 126(2), 729–734.