Circulating immune complexes in lupus erythematosus, scleroderma and dermatomyositis.

Circulating immune complexes (CIC) were measured by three different methods in serum from 17 patients with systemic lupus erythematosus (SLE), 3 patients with "hydralazine-induced" SLE-like syndromes, 14 patients with discoid lupus (DLE), 8 patients with systemic sclerosis and 5 patients with dermatomyositis. Immune complexes were detected in 13 of the 17 patients with SLE. All patients with lupus nephritis and typical exanthema had circulating immune complexes. The concentration of immune complexes was inversely correlated to serum complements C4 and C3. All 3 patients with "hydralazine-induced" SLE-like syndromes had circulating immune complexes that disappeared after withdrawal of the drug. Immune complexes were detected in 3 of the 14 patients with DLE; all 3 patients with CIC had wide-spread DLE. In systemic sclerosis, CIC were detected in only 1 of the 8 patients. Four of the 5 patients with dermatomyositis demonstrated CIC in serum. No complement consumption was detected in dermatomyositis and the immune complexes may have been secondary to tissue destruction.