Control of the immune response: role of macrophages in regulation of antibody-and cell-mediated immune responses.

The ability of peritoneal macrophage subpopulations, separated into different classes according to their size, to reconstitute antibody or cellular immune responses in macrophage-depleted spleen cells has been investigated. Data are presented to show that whether reconstitution is by "normal" or "activated" macrophages, be they syngeneic or allogeneic to the lymphocyte source, different populations reconstitute antibody and cellular immunity. Reconstitution is in general by two classes of macrophages, small and large. The former seem to reconstitute only if syngeneic to the responding lymphocyte pool, whereas large macrophages reconstitute immune responses from allogeneic lymphocytes as well as syngeneic lymphocytes. Evidence is also presented to show that syngeneic large macrophages can determine the type of immune response reconstituted; that is, with greater numbers of large cells only cytotoxic responses (and not T-dependent antibody formation) were reconstituted and vice versa.