Relation of clinical activity of rheumatoid arthritis to immune complexes, complement components and anti-immunoglobulins.

Circulating immune complexes by fluid phase Clq binding assay, complement components and anti-immunoglobulin levels were studied in sera of 35 patients with rheumatoid arthritis (RA). In 23 of the 35 sera (65.7%), circulating immune complexes were positive, and the mean +/- SD of Clq binding activity (ClqBA), 44.5 +/- 19.4%, was significantly high compared to that of healthy persons, 17.4 +/- 8.2%. Antigenic determination of complement components revealed that Clq, C3, C5, C9, factor B and Cl esterase inhibitor (ClINH) were significantly high in sera of RA, but C4 and properdin were not. The disease activity correlated with ClqBA, IgG- and IgM-anti-immunoglobulins, C9 and serum IgG. On the other hand, ClqBA correlated with both IgG- and IgM-anti-immunoglobulin levels but not with complement components.