Effect of rheumatoid factors and normal human sera on immune complex-Fc gamma R interaction

The results of this study demonstrate that inhibition of antibody-dependent cell-mediated cytotoxicity (ADCC) of human peripheral blood mononuclear cells (PBMC) by ovalbumin (OA)-IgG anti-OA immune complexes (IC) can be affected by rheumatoid factors (RF). Thus, pre-incubation of IC with IgM RF reduced the blocking effect of IC on IgG-Fc receptors (FC gamma R) measured by ADCC activity. However, the opposite effect could be observed when IgM RF was added after IC-Fc gamma R interaction. IgG RF did not modify these interactions significantly. In a previous report it was demonstrated that normal human sera (NHS) lead to recovery of the ADCC activity of PBMC that had been previously blocked by IC. IgM RF enhanced the recovery of ADCC by NHS, while IgG RF did not alter, or slightly decreased the ability of NHS to restore ADCC. These effects correlated with the different capacities of RF to activate complement (C). The results obtained show a new effect of RF on the regulation of immune mechanisms.