S-antigen-like protein in porcine ciliary epithelium

A soluble protein with a molecular weight of approximately 52,000 Da (from SDS-polyacrylamide gel electrophoresis) was purified from porcine ciliary body, vitreous body and retina by ammonium sulfate fractionation, Sephacryl S-300 gel filtration, and DEAE-cellulose ion exchange chromatography. The protein has a higher molecular weight than bovine S-antigen which is a highly pathogenic retinal antigen, and was eluted from DEAE-cellulose at a slightly higher NaCl concentration than the concentration at which bovine S-antigen was eluted. By reaction with anti-bovine S-antigen polyclonal antibodies, the porcine protein and bovine S-antigen showed full immunological identity. Using a panel of five monoclonal antibodies (MAbs) directed against epitopes spanning the entire length of bovine S-antigen, the porcine protein was analyzed by the enzyme immunoassay and found to react with all MAbs except one that is specific for a species-specific epitope of bovine S-antigen. Immunocytochemical labeling of porcine ciliary body using all of the MAbs demonstrated that the 52,000-Da protein was primarily localized to the nonpigmented epithelial cells rather than the pigmented epithelial cells. Consistent with this localization, the 52,000-Da protein was synthesized by in vitro translation of mRNA extracted from the nonpigmented cells. When injected into Lewis rats, the porcine protein was found to be far less effective in inducing uveoretinitis than native bovine S-antigen.