Immune complexes in systemic sclerosis; detection by C1q binding, K-cell inhibition and Raji cell radioimmunoassays.

Thirty-four patients with systemic sclerosis (SS) were investigated for the presence of circulating immune complexes by means of a fluid phase C1q binding assay, K-cell inhibition assay and a Raji cell radioimmunoassay and the results compared with those obtained in 21 patients with systemic lupus erythematosus (SLE) and 52 normal healthy controls. Patients with SS showed an incidence of circulating immune complexes comparable to that found in SLE, with 20 patients (58.5%), giving a positive result with at least one of the assays. The presence of circulating immune complexes in patients with SS was found to be associated with both elevation of serum IgG and IgA levels and extensive visceral involvement by the disease. These findings raise the possibility that circulating immune complexes could be involved in the pathogenesis of SS.