Localization of S-antigen by enzyme-labelled antibody method and electron microscopy.
Localization of S-antigen was studied by a direct enzyme-labeled immunohistochemical method with light and electron microscopes. IgG was prepared from rabbits which were sensitized by swine retinal S-antigen and the IgG was conjugated with horseradish peroxidase (HRP). This HRP-labeled IgG was directly applied to normal rabbit retina and the retina was processed to make slides for light and electron microscopic examinations. In light microscopic findings, a clear-cut positive response was noted in the outer segment of photoreceptor cells which was similar to that of Wacker's observation, and a weak response was observed in the inner segment of the photoreceptor cells and the outer nuclear layer. In electron microscopic findings, immunoprecipitates, which were represented by electron-dense particles, were observed on both sides of the disk membrane of the outer segment with evenly distributed particles on both outer and inner surfaces, showing a pattern symmetric to that of the membrane. These immunoprecipitates were also noted in the plasma membrane of the outer segment but there they did not show a pattern similar to that of the disk membrane. A small amount of pinpoint-shaped immunoprecipitates were also noted in the cytoplasm of the inner segment and the connecting cilia. The immunoprecipitates were observed to gradually decrease in number with the phagocytosis of the outer segment by the retinal pigment epithelium, and they finally disappeared as fragments which were completely phagocytized. These findings may suggest a renewal process of S-antigen and a rationalization of this theory was discussed.