Ultrastructural pathology of S-antigen uveoretinitis.

The morphology of S-antigen-induced uveoretinitis in guinea pigs has been studied using transmission electron microscopy. Purified bovine retinal S-antigen was shown to produce a focal chorioretinitis, characterized by selective damage to the outer retina and, almost exclusively, a mononuclear cell infiltration of the choroid and retina. Even at high doses, extensive rod outer segment damage was associated predominantly with lymphocytic and mononuclear cell infiltration. A single immunizing injection of S-antigen was sufficient to produce a chronic ocular inflammation lasting many months. Focal lesions evolved rapidly and reached an end-stage within days to weeks. Accordingly, eyes examined at any time during the disease contained areas of normal retina coexistent with fibrotic lesions. With time, the number of advanced or end stage lesions became more frequent, thereby involving a more widespread area of the retina. Examination of early stage lesions suggest that the rod outer segment is the target for immune damage in this disease, but the mechanism of damage remains to be elucidated.