| Abstract: | Objective Anti–RNA polymerase I/III (anti–RNAP I/III) antibodies are clinically useful markers of scleroderma, and their presence is associated with diffuse skin disease and an increased risk of cardiac and kidney involvement. Although RNAP I antibodies localize to the nucleolus, nucleolar staining by many anti‐RNAP antibody–positive sera is not always observed. Nucleolar staining by anti‐RNAP antibody–positive sera was examined by double staining with antifibrillarin antibodies to evaluate whether nucleolar staining can be used as a screening test for anti–RNAP I/III antibodies. In addition, the relationships between nucleolar staining and levels of anti–RNAP III antibodies were examined by enzyme‐linked immunosorbent assay (ELISA) and immunoprecipitation (IP) assay. Methods Sera were tested using immunofluorescent antinuclear antibodies on HEp‐2 cell slides, by anti–RNAP III ELISA, and by IP assay using 35S‐labeled K562 cell extract. Nucleolar staining by anti‐RNAP antibody IP‐positive sera was confirmed by double staining using antifibrillarin monoclonal antibodies. The levels of anti–RNAP III antibodies were quantitated by ELISA and by IP assay using a serially diluted reference serum as a standard, and their relationship was analyzed. Results All 18 anti–RNAP I/III antibody–positive sera showed nuclear speckled patterns, but nucleolar staining was readily noticeable in only 44% of the sera. A positive correlation was found between ELISA and IP units for anti–RNAP III antibodies. The levels of anti–RNAP III antibodies and anti–RNAP I antibodies correlated well, with the exception of a few sera. Levels of anti–RNAP III antibodies were low in sera with nucleolar staining, whereas several sera with high levels of anti–RNAP I antibodies clearly showed nucleolar staining. Conclusion Although some sera positive for anti–RNAP I/III antibodies clearly stain nucleoli, nucleolar staining is inconsistent and cannot be used to screen for anti–RNAP I/III antibodies. |
