S-antigen immunoreactivity in retinal rods and cones and pineal photosensitive cells.

The S-antigen is a protein of photoreceptors, mainly known for its autoantigenic properties in mammals, which is widely distributed in the retina of vertebrates and in photoreceptor organs of invertebrates. Using three monoclonal antibodies specific for different epitopes of S-antigen, this study complements our previous data on retinal rods and cones and presents new results on the photosensory cells of the pineal complex. Immunoreactivity was found in (i) retinal rods and cones, (ii) cone-like and modified photoreceptor cells, and pinealocytes of the pineal organ of vertebrates, (iii) cone-like photoreceptors of the frontal organ of the frog and of the third eye of the lizard. According to the species and the antibody used, some differences were found at the level of the cellular compartments of the pineal photoreceptor cells.