Anti-RNA polymerase III antibodies in patients with systemic sclerosis detected by indirect immunofluorescence and ELISA

Objectives. To evaluate the analytical performance of an ELISA for the detection of anti-RNA polymerase III antibody (ARA) and to assess IIF as a method for identifying this antibody. Methods. A commercially available ELISA was used to assess the presence of ARA in sera from 1018 SSc patients. The sera had been divided into sub-populations based on the presence of specific autoantibodies, ANA pattern or the absence of both. Patients with ARA (n = 209) had been identified by characteristic ANA pattern by IIF on HEp-2 cell substrate [and additionally by radio-immunoprecipitation (IP) in 157/209 cases]. The remaining 809 SSc patients acted as a control group. Results. Of 157 patients in whom ARA had been confirmed by IP, 150 were positive by ELISA providing a sensitivity of 96%. In the group where ARA had only been assessed by IIF, 100% (52/52) were ELISA positive. The ANA patterns indicating the presence of ARA were a fine-speckled nucleoplasmic stain with additional occasional bright dots, with or without concurrent punctate nucleolar staining. In the SSc control group, the ELISA attained a specificity of 98%, ARA being detected in 17/809 patients. Conclusions. We report the outcome of a study on a large population of SSc patients that shows the ARA ELISA to be of high analytical sensitivity and specificity. We confirm that there is minimal overlap between ARA and other SSc-specific autoantibodies. Additionally, it is demonstrated that the presence of ARA correlates with identifiable patterns by IIF on HEp-2 cell substrate.