Evidence for intrinsic cellular defects of 'complement' receptor-mediated phagocytosis in patients with systemic lupus erythematosus (SLE).

Fc and 'complement'-mediated phagocytosis of pre-opsonized yeast has been studied in monocytes from 18 patients with SLE. Monocytes from nine of 18 patients had depressed complement-mediated phagocytosis (P = 0.0001, Fishers exact test) but only three of 18 had depressed Fc-mediated phagocytosis (NS, Fishers exact test). Although reduced complement-mediated phagocytosis was correlated with increased frequency of disease manifestations (P less than 0.003, rank correlation) there was no correlation with serum DNA or C1q binding activity, C3 or C4 levels. Serum from SLE patients with depressed phagocytosis did not inhibit phagocytosis by normal monocytes. The data suggests the presence of intrinsic abnormalities of monocyte receptor function in SLE and the nature of the 'complement' receptors involved is discussed.