Metabolism of factor B of serum complement in rheumatoid arthritis.

An increased rate of catabolism of radio-iodinated Factor B has been shown in five out of ten patients with rheumatoid arthritis. Serum levels of Factor B were normal, the increased catabolism being matched by increased synthesis. The patients showing high catabolic rates had more manifestations of extra articular disease than did those with normal catabolic rates and they had higher rheumatoid factor titres. In seven patients, the catabolic rate for Factor B correlated significantly with the rate of IgG catabolism. In this series, the Raji-cell assay for immune complex-like material was in the normal or near normal range in all but one patient.