Immunopathology of pineal glands from horses with uveitis

PURPOSE. Pinealitis accompanying uveitis is well established in laboratory models of experimental autoimmune uveoretinitis. In naturally occurring uve itis, pinealitis has been demonstrated in the pineal gland from a mare with active uveitis and is suspected in some human uveitides. We have evaluated pineal glands from horses with various stages of uveitis for signs of immu nopathology accompanying spontaneous uveitis. METHODS. Pineal glands from 10 horses with uveitis and from 13 horses witho ut uveitis were evaluated for histochemical (H&E, collagen) and immunohisto chemical (MHC class II. antigen expression, infiltration of T and B lymphoc ytes, and glial fibrillary acidic protein (GFAP) and vimentin upregulation) evidence of inflammation. RESULTS. Septal areas of pineal glands from horses with uveitis had cluster s of MHC class II antigen-expressing cells, T lymphocytes, and enhanced col lagen deposition. These changes were not as readily observed in pineal glan ds from horses without uveitis. B lymphocytes were detected only in the pin eal gland from the one mare with active uveitis in which T and B lymphocyte s were organized into follicles. No differences in GFAP or vimentin immunor eactivity were noted in pineal glands from horses with or without uveitis. CONCLUSIONS. These pineal gland changes suggest that the pinealitis associa ted with equine uveitis is transient just as the uveitis of these horses is recurrent. Study of pineal glands from horses with clinically documented u veitis allows demonstration of subtle pineal changes associated with natura l uveitis. Similar changes would be difficult to document in human patient populations.