Monocyte in vitro function in systemic lupus erythematosus (SLE). I. A clinical and immunological study.

A previous article (34) has shown that normal monocytes cultivated in presence of several sera from patients with SLE displayed low yeast cell phagocytosis. In the present extended study it was investigated whether the level of phagocytic activity (PA) had any relation to clinical and laboratory expressions of disease activity. The results reveal that, in addition to hypocomplementaemia and cryoglobulinaemia, low PA was associated with high clinical disease activity including arthritis, rash and nephritis and high titres for anti-nDNA. It was also found that PA improved as the disease activity declined. These findings suggest that this in vitro phagocytosis test might be used as an indirect method for detecting clinically relevant circulating immune complexes in SLE. Furthermore, it might be used as a guide in the evaluation of disease activity in severe SLE. The mechanism behind impaired phagocytosis was not elucidated in this study. Inadequate opsonization of the yeast cells or blocking of the monocyte surface receptors by immune complexes were suggested as possible explanations.