Demonstration of antibodies to soluble nuclear antigens by complement fixation test. An application of microtiter technique.

The complement fixation test utilizing the microtiter system was applied to study sera from patients with a variety of connective tissue diseases for the presence of antibodies to soluble nuclear antigens. A good correlation was found between microtiter complement fixation and hemagglutination for anti-RNP and anti-Sm antibodies. Anti-Ha antibodies were detected by complement fixation but not by hemagglutination. Different enzyme digestions of the soluble nuclear antigen prior to assay and use of a quantitative microcomplement fixation test were found to improve the analysis of sera with multiple antibodies.