SERA FROM PATIENTS WITH RHEUMATIC DISEASES RECOGNIZE DIFFERENT EPITOPE REGIONS ON THE 52-KD RO SS-A PROTEIN

Patients suffering from systemic lupus erythematosus (SLE) or Sjogren' s syndrome (SS) often contain autoantibodies directed to the Ro(SS-A) complex. In this study the antigenic determinants on two of the compon ents of the Ro complex, i.e. the Ro60 and the Ro52 polypeptides, were investigated. Anti-Ro+ sera were selected by counter-immunoelectrophor esis. Depending on the detection method, 59-68% of the SLE patients pr oduced anti-Ro but not anti-La antibody, while 72-81% of the SS patien ts produced both anti-Ro and anti-La antibody. Immunoprecipitation of recombinant Ro-proteins showed that 61 sera (87%) were reactive with b oth Ro proteins, seven sera with Ro60 only, one serum with Ro52 only, and one serum did not precipitate the proteins at all. The anti-Ro60 r eactivity of human sera is strongly associated with the native form of Ro60, suggesting that conformational autoepitopes are an important fe ature of Ro60. In the case of Ro52, frequently the residues located be tween amino acids 216 and 292 were essential for reactivity with the a ntibodies. With 70% of the lupus sera tested this appeared to be the o nly region important for reactivity. The antibodies of SS patients gen erally recognized multiple B cell epitopes located between amino acids 55 and 292. The results of this study indicate that the antigenic det erminants on Ro52 are different for autoantibodies produced by lupus p atients compared with those of SS patients.