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.