Inhibition of complement-mediated hemolysis in gel by rheumatoid factors

When subjected to a hemolysis in gel (HIG) assay for the detection of complement deficiency, 9 of 37 sera from patients with classical rheumatoid arthritis produced impaired lysis of sensitized sheep erythrocytes. All sera were normal in a test for the alternative pathway and no major abnormalities were found within the complement system. Using a two-step HIG technique, with guinea-pig serum as the complement source, all sera were shown to inhibit lysis of sheep erythrocytes sensitized with rabbit IgG. Lysis of IgM-coated erythrocytes was not inhibited. The agglutination titers in a Waaler-Rose test, and the areas of inhibition in the two-step HIG assay with IgG-sensitized erythrocytes, were correlated (r = 0.80, p less than 0.001). Absorption of serum with rabbit IgG coupled to Sepharose 4B, reduced the capacity to inhibit immune hemolysis. The eluate from IgG-Sepharose contained rheumatoid factors and also inhibited immune hemolysis. The findings suggested that rheumatoid factors in serum were responsible for inhibition in the HIG assays used.