Functional heterogeneity of macrophages: subclasses of peritoneal macrophages with different antigen-binding activities and immune complex receptors.

Cell suspensions prepared from 24-hour cultures of adherent peritoneal exudate cells from rabbits were separated into density subclasses on discontinuous gradients of Ficoll. Of the five subclasses obtained, macrophages comprised over 95 per cent of the cells in the two least dense subclasses and over 90 per cent of the cells in the subclasses of intermediate density. The most dense subclass contained approximately 80 per cent macrophages and 20 per cent lymphocytes. The antigen-binding properties of the subclasses were studied with a selected number of I-labelled antigens in the presence and absence of added antibodies. In the absence of antibody the subclasses differed from one another in antigen-binding activities; these differences were independent of both the test antigens and the state of antigen aggregation. In the presence of specific antibody, two macrophage subclasses bound substantially more antigen than the other subclasses. The enhanced responses of these subclasses were confirmed by studying the cells' capacity to form rosettes when incubated with sensitized chicken erythrocytes. The results indicated that macrophages in these two subclasses differed quantitatively and/or qualitatively from other macrophage subclasses with regard to immunoglobulin receptor sites. These studies demonstrate the feasibility of using gradient separation procedures to obtain functionally distinct subclasses of cells rich in macrophages. The availability of well-defined macrophage populations should permit more precise studies of macrophage functions in immunity.