Fixation of complement by anti-F(ab')2 antibodies or ssDNA when added to systemic lupus erythematosus sera

A solid phase total hemolytic complement assay was used to quantitatively determine the % complement fixation by anti-F(ab')2 antibodies or ssDNA when added to serum from patients with systemic lupus erythematosus (SLE). Both autologous and homologous anti-F(ab')2 antibodies with demonstrated anti-anti-ssDNA activity fixed complement when added to SLE sera and normal human complement. Furthermore, comparable amounts of anti-F(ab')2 antibodies with minimal anti-anti-ssDNA activity fixed zero or minimal amounts of complement when added to the same lupus sera. When measured by the same assay with the same sera, ssDNA fixed greater amounts of complement than did comparable amounts of any of the anti-F(ab')2 antibodies.