SS-A/Ro antibodies in Chinese patients with systemic lupus erythematosus and Sjögren's syndrome

Serum from 53 patients with systemic lupus erythematosus (SLE) and 23 patients with primary Sjögren's syndrome (SS) were studied for anti-52-kDa SS-A/ Ro, anti-60-kDa SS-A/Ro, and anti-SS-B/La antibodies by immunoblotting and enzyme-linked immunosorbent assay (ELISA). By immunoblotting, anti-SS-A/Ro was detected in 16 (30%) patients with SLE and 17 (74%) patients with SS. Anti-SS-B/La was detected in 22 (41%) patients with SLE and 15 (65%) patients with SS. Serum from 14 of the 16 SLE patients with anti-SS-A/Ro reacted with the 60-kDa protein and 15 serum samples from these patients recognized the 52-kDa protein. Serum with anti-60-kDa SS-A/Ro alone was not found. Serum from all of the 17 SS patients with anti-SS-A/Ro reacted with the 52-kDa protein, whereas serum from only two of these patients recognized the 60-kDa protein. By ELISA, the frequency of anti-SS-A/Ro (antibodies to the 60-kDa and/or 52-kDa of SS-A/Ro proteins) in patients with SLE and SS was 43/53 (81%) and 15/23 (65%), respectively. Anti-48-kDa SS-B/La was found in 28% and 48% of SLE and SS patients, respectively. Serum from 77% of SLE patients and 48% of SS patients reacted with the 60-kDa SS-A/Ro protein. Serum from 45% of SLE patients and 52% of SS patients reacted with the 52-kDa SS-A/Ro protein. Patients with SLE had significantly higher titers of antibodies to 60-kDa SS-A/Ro compared with patients with SS. Anti-SS-A/Ro and anti-SS-B/La are common in both SLE and SS. The different reactivities of anti-52-kDa and anti-60-kDa antibodies in serum from patients with SLE and SS may represent differences in conformation-dependent epitopes of SS-A/Ro autoantigens.