ANTIBODIES TO EYRKK VESICULAR STOMATITIS VIRUS-RELATED PEPTIDE ACCOUNT ONLY FOR A MINORITY OF ANTI-RO60KD ANTIBODIES

Previous studies demonstrated a possible antigenic relation between th e carboxyl terminal portion of anti-Ro60kD autoantigen and a nucleocap sid protein (N) of vesicular stomatitis virus (VSV). In order to inves tigate whether anti-Ro60kD autoantibodies react with the VSV homologou s region of the Ro60kD protein we synthesized, according to Merrifield 's method, the EYRKKMDI octapeptide (8p) sharing a common sequence wit h the N protein of VSV. Sera from 61 patients with autoimmune rheumati c diseases (34 systemic lupus erythematosus (SLE), 21 Sjogren's syndro me (SS) and six rheumatoid arthritis (RA)) as well as 59 from normal b lood donors were tested for the presence of anti-Ro60kD autoantibodies by ELISA and immunoblot (IB) and anti-8p antibodies by ELISA. Antibod ies to 8p were found in 9/31 of anti-Ro60kD IB-positive sera, 5/30 of anti-Ro60kD-negative sera and 2/59 of normal control sera. The concord ance between the anti-8p ELISA and the anti-Ro60kD IB was very poor (c hi(2) = 0.71, P = 0.4) in contrast to the anti-Ro60kD ELISA and the an ti-Ro IB (chi(2) = 27.6, P = 10(-7)). Subsequent affinity purification of the anti-8p antibodies from a strong positive anti-8p and anti-Ro6 0kD SLE serum yielded 95% depletion of the anti-8p activity and 37% re duction of the anti-Ro60kD activity. Inhibition assays with the affini ty-purified anti-8p antibodies demonstrated that the octapeptide gave 94.5% inhibition of the anti-Ro60kD activity, while Ro60kD protein led to 42.3% inhibition of the anti-8p. Preincubation of the serum with t he octapeptide produced 4% inhibition of anti-Ro60kD ELISA. These resu lts indicate that the anti-8p antibodies account only for a minority o f the anti-Ro60kD autoantibodies.