Alveolar macrophage stimulation of T-cell proliferation in autologous mixed lymphocyte reactions. Role of HLA-DR antigens.

Alveolar macrophages act as accessory cells in lymphocyte response to mitogens or alloantigens. Because the autologous mixed lymphocyte reaction (MLR), in which HLA-DR-positive non-T cells stimulate the proliferation of autologous T lymphocytes, represents a good model to study macrophage-T cell interaction, we examined and compared the ability of human alveolar macrophages and peripheral blood-derived monocytes to induce T-cell proliferation in autologous MLR. Maximal T lymphocyte proliferation was observed in both alveolar-macrophage- and blood-monocyte-stimulated autologous MLR at a T cell to alveolar macrophage or blood monocyte ratio of 4:1, but the ability to stimulate T-cell proliferation was lower for alveolar macrophages than for blood monocytes (p less than 0.01). Because HLA-DR antigens modulate monocyte-T cell interaction, we quantified the proportions of HLA-DR-positive cells in alveolar macrophage and blood monocyte suspensions and determined the inhibitory effects on T-cell proliferation of masking HLA-DR antigens on stimulator cells with monoclonal antibodies. The proportions of HLA-DR-positive cells were higher in alveolar macrophage than in blood suspensions (p less than 0.01); interestingly, however, the preincubation of the stimulator cells with anti-HLA-DR monoclonal antibodies inhibited to a similar extent both alveolar-macrophage- and blood-monocyte-stimulated autologous MLR (p greater than 0.2). These studies indicate that alveolar macrophages are less effective than blood monocytes are as stimulator cells in autologous MLR and that, although the masking of HLA-DR molecules results in inhibition of autologous MLR, T-cell proliferation is not dependent on the numbers of stimulator cells bearing HLA-DR antigens. The autologous MLR may represent a good model to study the functions of alveolar macrophages during their interaction with autologous T cells in health and disease.