Objective: We have recently developed an enzyme-linked immunosorbent assay (ELISA) for detection of anti-RNA polymerase III (anti-RNAP III) antibody, using a recombinant fragment containing the immunodominant epitope as the antigen source. This study was conducted to assess the analytical accuracy and clinical associations of the anti-RNAP III ELISA in patients with systemic sclerosis (SSc).
Methods: To evaluate analytical sensitivity and specificity of the ELISA, both immunoprecipitation tests and ELISA were used to detect anti-RNAP III antibody in 534 SSc sera from patients at 3 medical centers. Sera from 522 SSc patients and 516 controls, including patients with other connective tissue diseases and blood bank donors, were also evaluated to assess the clinical sensitivity and specificity of the ELISA. Clinical findings in anti-RNAP III antibody-positive SSc patients were compared between patient groups stratified according to anti-RNAP III antibody levels determined by the ELISA.
Results: In SSc patients, our ELISA showed analytical sensitivity of 91% and analytical specificity of 99% compared with the immunoprecipitation assay (a gold standard for detection of anti-RNAP III antibody). The additional analysis using a large series of SSc and control sera showed that clinical sensitivity and specificity of the ELISA with respect to the diagnosis of SSc were 17% and 98%, respectively. A high level of anti-RNAP III antibody was associated with diffuse cutaneous SSc, higher maximum total skin score, and increased frequency of tendon friction rubs.
Conclusion: The anti-RNAP III ELISA is analytically accurate and clinically specific. With this assay, testing for anti-RNAP III antibody can be made routinely available.