Serum antibody levels to retinal S-antigen determined by ELISA in experimental and human uveitis

Retinal S-antigen is thought to play an important role in the immunopathogenesis of uveitis. To investigate the role of S-antigen in human uveitis, an immunopotent bioactive S-antigen and a sensitive enzyme-linked immunosorbent assay (ELISA) were developed to determine the anti-S-antigen antibody contents in experimental autoimmune uveitis (EAU) and human uveitis. The bovine S-antigen was isolated by ammonium sulfate precipitation, Fractogel TSK HW-55 gel filtration and hydroxylapatite absorption chromatography. A test by SDS polyacrylamide electrophoresis showed that it was a highly purified protein. The purified S-antigen evoked EAU in 60% of eyes of guinea pigs even at the dose of 1 microgram. ELISA was developed to determine the contents of serum immunoglobulin G antibody against S-antigen. In the serum of S-antigen immunized rabbit, the antibody was measurable up to 1:160,000 in dilution. The antibody content appeared on the 10th day following inoculation and rose gradually until the 22nd day when the maximal antibody content was observed. Regarding human uveitis, the anti-S-antigen antibody was higher in 31 patients with Behçet's disease and 8 with Harada's disease than in normal controls although statistical significance existed only in the former (p less than 0.02). In this study, the method to purify the bovine retinal S-antigen proved relatively rapid and efficient. The ELISA developed herein appeared sensitive and well reproducible in the detection of anti-S-antigen antibody. The results showed that retinal autoimmunity may play a role in the pathogenesis in EAU and human uveitis.