Clinical significance of circulating immune complex assay in patients with systemic lupus erythematosus.

Circulating immune complexes (IC) were assayed in 65 patients with systemic lupus erythematosus (SLE), 34 patients with rheumatoid arthritis (RA), 40 patients with progressive systemic sclerosis (PSS), 35 patients with chronic glomerulonephritis (GN) and 30 healthy controls. Immunoglobulin components of PEG-precipitated IC from 10 patients with SLE were also determined. Cryoglobulins isolated from 11 patients with SLE were assayed for their IC-like activity. The effect of corticosteroid treatment on IC levels were also studied in SLE patients with nephritis. IC levels significantly increased in all groups but those of SLE patients were the highest values. The SLE patients with nephritis had higher levels than those without renal involvement. IgG- d IgM- but no IgA-components were found in 100% and, 90%, respectively, of IC preparations. IC-like activity of cryoglobulins were found to correlate with disease severity and appeared to be characteristic of clinical manifestations. Corticosteroid therapy significantly decreased IC levels, however, related to the entire patient group, the mean of IC level was still higher than that of healthy controls. The degree of IC level decrease (as percentage), but not absolute values, appeared to be significant in assessing disease activity. The clinical significance of IC determination and IC activity of cryoglobulins are discussed.