NONPRECIPITATING ANTI-LA(SS-B) AUTOANTIBODIES IN PRIMARY SJOGRENS-SYNDROME

Anti-La(SS-B) precipitin-negative sera show a restricted epitope recog nition and can be easily overlooked in routine laboratory testing. We have therefore determined the prevalence of nonprecipitating anti-La(S S-B) antibodies in patients with primary Sjogren's syndrome and studie d their clinical and immunological associations. Clinical details were obtained from 68 patients with primary Sjogren's syndrome, and serum samples were examined by enzyme-linked immunosorbent assay using purif ied recombinant La, 60-kDa Po, and 52-kDa Ro proteins and by counterim munoelectrophoresis. Thirteen patients (19%) were identified with anti -La antibodies which were nonprecipitating. These patients had similar clinical findings to other groups of patients with Sjogren's syndrome , but had significantly lower rheumatoid factor and serum IgG levels t han patients with anti-La precipitins. None of the patients with nonpr ecipitating anti-La antibodies had previously contained anti-La precip itins in their sera. Furthermore, they tended to have lower levels of antibodies directed against denatured 60-kDa Ro (but not 52-kDa Ro) co mpared with anti-La precipitin-positive patients. Patients with Sjogre n's syndrome associated with nonprecipitating anti-La antibodies repre sent a stable serological and clinical subset in which there appears t o be limited diversification of the autoimmune response to the Ro60 an d La proteins of the Ro/La ribonucleoprotein. (C) 1996 Academic Press, Inc.