Evidence for defect of complement-mediated phagocytosis by monocytes from patients with rheumatoid arthritis and cutaneous vasculitis.

In-vitro measurements of the rate of monocyte phagocytosis of heat-killed yeast preopsonised in human AB serum from 14 patients with rheumatoid arthritis and 14 normal controls showed a significant reduction in five patients with active vasculitis but no change in nine with active arthritis alone. Further studies of complement- and Fc-mediated monocyte phagocytosis in which the rate constants (Kc and KFc respectively) were determined using complement-coated Saccharomyces cerevisiae and Candida albicans opsonised with IgG in monocytes from nine patients with rheumatoid vasculitis and 12 controls showed a significant reduction in Kc (p less than 0.01) but normal KFc. Kc was normal in three patients with inactive vasculitis. Low Kc was correlated with low serum C3 concentrations but not with Clq binding or anticomplementary activity, and no evidence of intracytoplasmic or membrane-bound immune complexes was detected in monocytes from patients with active vasculitis. These results show that cutaneous vasculitis in rheumatoid arthritis is associated with selective impairment of complement-mediated monocyte phagocytosis, which does not appear to result from receptor blockade by immune complexes.