S-antigen in a hereditary visual cell disease. Immunocytochemical and immunological studies

S-antigen is a photoreceptor-specific and potentially autoantigenic protein. Using light microscopic immunocytochemistry, the localization of S-antigen was studied in the retinas of normal dogs and Irish setters affected with rod-cone dysplasia, a hereditary retinal degeneration characterized by abnormal cGMP metabolism and arrested outer segment differentiation. Normal and affected dogs were also tested for the presence of humoral and cellular immunity to S-antigen. S-antigen was present in both rods and cones during inner and outer segment differentiation, but there was an apparent loss of immunoreactivity in cones as the retina matured. The developmental appearance and localization of S-antigen in affected retinas was similar to that of normals. S-antigen immunoreactivity decreased during the early stages of rod loss (39-57 days), but was still present in photoreceptor somata in the late stages of retinal degeneration. No significant difference was found between normal and affected setters in humoral immunity to S-antigen, indicating that it probably does not stimulate autoimmunity in red 1. Because normal dog lymphocytes failed to respond when sensitized to bovine S-antigen, cellular immunity to S-antigen in this disease cannot be ruled out.