A comparison of the regulatory effects of human monocytes, pulmonary alveolar macrophages (PAMs) and spleen macrophages upon lymphocyte responses.

Human monocytes, pulmonary alveolar macrophages (PAMs) and spleen macrophages were concentrated by immobilization on cold insoluble globulins. These cell preparations were 90 +/- 3%, 95 +/- 1% and 83 +/- 3% esterase rich, respectively, 87 +/- 4%, 95 +/- 3% and 66 +/- 11% phagocytic and 78 +/- 3%, 79 +/- 9% and 68 +/- 5% reactive with OKM1 monoclonal antibody. Spleen macrophages differed from the other two cell preparations in that significantly fewer reacted with 61D3 or 63D2 monoclonal antibodies. Monocytes and PAMs promoted the mixed leucocyte response by autologous lymphocytes when added at low concentrations, but suppressed this response at high concentrations. Spleen macrophages only promoted the mixed leucocyte reaction but were required in much higher numbers than either monocytes or PAMs for optimal promotion. Likewise, the added presence of monocytes or PAMs in high numbers suppressed Ig synthesis stimulated with pokeweed mitogen, while spleen macrophages were not suppressive in this system. This study shows that the distribution of macrophages that differ in their regulatory effects upon lymphocyte responses varies in different tissues. The human spleen is deficient in macrophage related suppression.