Ultrastructural localization of retinal S-antigen in the rat

Using a peroxidase-antiperoxidase immunohistochemical technique, the light and electron microscopical localization of retinal S-antigen was demonstrated in the rat retina, using antisera to bovine and guinea pig S-antigen. Comparable localization of S-antigen was observed with both antisera, although in our hands, the antiserum to bovine S-antigen gave more intense immunostaining. By light microscopy, the most intense immunoreactivity to retinal S-antigen was seen in the outer segment of the photoreceptor layer. Some immunostaining was also demonstrated surrounding the cell bodies of the outer nuclear layer. The inner segment of photoreceptors was virtually devoid of immunoreactivity. Ultrastructurally, immunoreactivity to S-antigen was demonstrated mainly on the inner surfaces of the visual discs of the rods. The plasma membranes of the outer segment of the rods were stained as well. Immunoreactivity surrounding the cell bodies of the outer nuclear layer was ultrastructurally localized on plasma membranes. The inner segment of the photoreceptor layer, other parts of the retina, or any eye structures other than retina showed no immunoreactivity. The relationship of retinal S-antigen to other cell components in the retina and the possible mechanisms of the autoimmune uveal diseases are discussed.