A full-length cDNA clone to human S-antigen (HS-ag) was isolated fromγgt 10 human retinal library and expressed as a fusion protein with glutathione S-transferase (GST) inE. Coli.Uveitogenicity and immunogenicity of recombinant GST-HS-ag fusion protein and native HS-ag were compared in EAU-susceptible Lewis rats.Recombinant HS-ag was found less uveitogenic than native HS-ag. Animals inoculated with recombinant HS-ag developed EAU on day 17, three days later than those inoculated with native HS-ag, the incidence of the disease was reduced from 80% to 58% and the score of clinical severity reduced from 2.2 to 1.3 points respectively. In contrast, rGST-HS-ag was more immunogenic than native HS-ag as it elicited four times higher levels of antibodies which reacted specifically with both antigens.