The immune response to the Ro(SSA) antigen is heterogeneous. Anti-Ro(SSA) positive sera may contain antibodies recognizing either a 60 or a 52 kDa polypeptide component of the Ro(SSA) particle. Thus we sought to determine the profile of anti-Ro(SSA) antibodies defined by immunoblotting in patients with rheumatic diseases.
Immunoblotting against human placenta extract and ELISA against recombinant Ro(SSA) antigen as confirmatory tests were done to detect anti-Ro(SSA) antibodies in 563 sera from patients with systemic lupus erythematosus (SLE). Sjögren's syndrome (SS), rheumatoid arthritis (RA) and other connective tissue diseases.
Anti-52 kDa antibodies were more common in primary patients with SS (9/22; 40.9%) than in patients with SLE (29/135; 21.4%) or patients with RA (7/315; 2.2%). Anti-60 kDa antibodies were more frequent in patients with SLE (26/135; 19.2%) than in patients with primary SS (2/22; 9%) or RA (17/315; 5.3%). None of the 22 patients with primary SS had only antibodies to the 60 kDa polypeptide. Among the 153 patients whose sera were positive by ELISA, 73 (47.7%) were negative by immunoblotting. The most frequent diagnoses in these sera were RA and SLE. The anti-52 kDa sera had higher optical density values compared to anti-60 kDa sera.
Our observations indicate the existence of qualitatively and quantitatively different anti-Ro(SSA) responses in the rheumatic diseases. The major responses are anti-52 kDa antibodies in primary SS, both anti-52 and anti-60 kDa antibodies in SLE, and anti-60 kDa antibodies in RA and other connective tissue diseases.