Circulating immune complexes and C1 activation in patients with rapidly progressive glomerulonephritis, before and after treatment with immunosuppression and plasma exchange.

Well-known assays for detection of circulating immune complexes (CIC) (C1 q binding assay, C1q deviation test, solid-phase C1 q binding assay, solid-phase conglutinin binding assay, and the platelet aggregation test) were used in 30 patients with different kinds of rapidly progressive glomerulonephritis. In 89% of the patients evidence of CIC was found in at least one of the assays. 81% of the patients were positive in the C1q binding assay and/or the conglutinin binding assay with addition of complement. CIC were more often detected by several assays, and with higher values in patients with systemic disease than in patients with renal involvement alone. CIC were found in 2 patients with Goodpasture's syndrome. 15 patients were reexamined after treatment with plasma exchange, when the disease was clinically inactive. The patients were still on immunosuppressive treatment. In most of these, CIC were detectable, but with lower values than at the start of treatment. Before treatment, high levels of C1r-C1s-C1 inactivator complexes suggested increased C1 activation in 93% of the patients. C-reactive protein was raised, and the concentrations of C1 q, C1s, C4, C3 and factor B were normal or high in most of the patients. Pronounced hypocomplementemia was found only in 2 patients with systemic lupus erythematosus (SLE). After treatment, the levels of C-reactive protein, C1 q, C1s, C3 and factor B had decreased in the non-SLE patients, while the average levels of C4 and C1r-C1s-C1 inactivator complexes were essentially unchanged.