Increased antibody-dependent cell-mediated cytotoxicity by monocytes from patients with rheumatoid arthritis.

Antibody-dependent cell-mediated cytotoxicity (ADCC) was studied in adult patients with rheumatoid arthritis (RA) and in healthy controls. Three effector cell populations from the peripheral blood were studied which included a mixed mononuclear population, a monocyte-depleted fraction, and a monocyte-enriched fraction. The monocyte-enriched fraction from patients with RA mediated a significantly increased degree of cytotoxicity. Enhanced cytotoxicity was more evident at low effector : target ratios. There was no significant difference in ADCC activity between patient cells and control cells when either the mixed mononuclear population or monocyte-depleted population was studied as effectors. The enhanced effector function of the peripheral blood monocyte in this system may be further indication that mononuclear phagocytes are "activated" in patients with RA.