Levels of anti-RNA helicase A (anti-RHA) versus other autoantibodies. IgG anti-U1RNP/Sm, ribosomal P (P peptide), double-stranded DNA (dsDNA), and β2 glycoprotein I (β2GPI) were determined by enzyme-linked immunosorbent assay. Serum dilutions used were 1:2,500 for anti-U1RNP/Sm and 1:500 for all others. Anti-RHA levels were semiquantified from immunoprecipitation using phosphorimager. (a) Anti-U1RNP/Sm antibodies. (b) Anti-P peptide antibodies. (c) Anti-dsDNA. (d) Anti-β2GPI. (e) Anti-RHA levels in anti-U1RNP/Sm-positive versus -negative sera. (f) Correlation of anti-RHA versus anti-U1RNP/Sm.