Characterization of antibody-dependent cell-mediated cytotoxicity in rheumatoid synovial fluid

Synovial fluids of 15 rheumatoid arthritis patients, 11 juvenile rheumatoid arthritis patients, and 6 patients with other chronic inflammatory joint diseases were studied. The isolated mononuclear cells, mainly monocyte/macrophages and lymphocytes, were preincubated overnight and then cultured with antibody-sensitized 51Cr-labelled chicken erythrocytes. There was no significant difference in the cytotoxicity between mononuclear cells from synovial fluid and peripheral blood of the patients. Depletion of adherent cells of the mononuclear cell suspensions by nylon wool column fractionation or by incubation on plastic dishes and depletion of cells which had phagocytosed colloidal iron had no substantial effect on the cytotoxicity whereas depletion of cells forming rosettes with human erythrocytes sensitized with human IgG (EA-RFC) practically abolished the activity. This shows that in rheumatoid synovial fluids the net effect of monocyte/macrophages in this in vitro antibody-dependent cytotoxic assay is small. Thus, the main effector cells in these mononuclear cell suspensions are lymphocytes which probably exhibit surface-bound Fc-receptors.