ABSTRACT The recent discovery and characterization of several proteins that purify with endogenous, bound retinoid have given rise to the suggestion that these proteins, which are abundant in retina, perform a role in transport and function of vitamin A. Immunocytochemical techniques were used to localize two retinoid-binding proteins in the retina of four species. Antisera to cellular retinal-binding protein (CRALBP) and an interphotoreceptor retinoidbinding protein (IRBP) were obtained from rabbits immunized with antigens purified from bovine retina. Antibodies from each antiserum reacted with a single component in retinal homogenates and supernatants which corresponded to the molecular weight and charge of the respective antigen (non-SDS and SDS PAGE, electrophoretic transfer to nitrocellulose, immunochernical staining). Immunocytochemistry controls were antibodies from nonimmune serum and antibodies absorbed with purified antigen. Antigens were localized on frozensectioned bovine, rat, monkey, and human retina using immunofluorescence and the peroxidase-antiperoxidase technique. Specific staining with anti-IRBP was found in the space that surrounds photoreceptor outer segments, with heaviest labeling in a line corresponding to the retinal pigment epithelium (RPE) apical surface. Cone outer segments were positive. Stainin
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