Inhibition of spontaneous and antibody-dependent cellular cytotoxicity by sera and isolated antiglobulin preparations from rheumatoid arthritis patients.

Using sera from patients with rheumatoid arthritis and antiglobulin preparations obtained from such sera, inhibition of human lymphocyte cytotoxicity in antibody-dependent (ADCC) and spontaneous cell-mediated cytotoxicity (SCMC) reactions against an allogeneic melanoma cell line (IGR3) has been demonstrated. Fractionation of effector cell preparations indicated that Fc-receptor-bearing lymphocytes were operative in both reactions. Removal of phagocytic and adherent cells from the effector cell population resulted in more pronounced inhibition of SCMC and ADCC reactions by rheumatoid sera. The results indicate that antiglobulin preparations from human sera containing rheumatoid factor activity can effectively block the cytotoxic activity of Fc-receptor-bearing effector lymphocytes (K cells) in vitro. On analogy with the inhibition of ADCC and SCMC reactions by immune complexes and aggregated IgG, antiglobulin complexes present in the antiglobulin preparations are responsible for this effect.