Electron immunocytochemical localization of retinal S-antigen with a rat monoclonal antibody.

This report describes the ultrastructural localization of S-antigen in pig and human retinas by means of a highly specific rat IgG monoclonal antibody, S2.4.C5, followed by a secondary antibody adsorbed to colloidal gold. This monoclonal antibody gave definitive staining with negligible background. The protein was detected in both the rod outer and inner segments. Connecting cilia and the rod outer segment disc membranes were labelled. The outer segment plasma membrane was not obviously labelled. Cones were labelled at background level. S-Antigen was not detected in any other cells of the neural retina. The fate of S-antigen was also followed to the pigment epithelial phagosomes where intracytoplasmic ROS debris was stained with the antibody. No label, however, was detected in the choroid, suggesting that trans-cellular transport of the S-antigen did not occur.