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 uveitis, 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 immunopathology accompanying spontaneous uveitis. METHODS: Pineal glands from 10 horses with uveitis and from 13 horses without uveitis were evaluated for histochemical (H&E, collagen) and immunohistochemical (MHC class II antigen expression, infiltration of T and B lymphocytes, and glial fibrillary acidic protein (GFAP) and vimentin upregulation) evidence of inflammation. RESULTS: Septal areas of pineal glands from horses with uveitis had clusters of MHC class II antigen-expressing cells, T lymphocytes, and enhanced collagen deposition. These changes were not as readily observed in pineal glands from horses without uveitis. B lymphocytes were detected only in the pineal gland from the one mare with active uveitis in which T and B lymphocytes were organized into follicles. No differences in GFAP or vimentin immunoreactivity were noted in pineal glands from horses with or without uveitis. CONCLUSIONS: These pineal gland changes suggest that the pinealitis associated with equine uveitis is transient just as the uveitis of these horses is recurrent. Study of pineal glands from horses with clinically documented uveitis allows demonstration of subtle pineal changes associated with natural uveitis. Similar changes would be difficult to document in human patient populations.

Retinal immunopathology in horses with uveitis.

BACKGROUND: Equine uveitis is a spontaneous disorder of horses that can serve as a model for the study of human uveitis. Although the initial presentation is that of an anterior uveitis, retinal involvement has been noted in some cases. We report here the immunohistopathology of retinas from horses with uveitis. METHODS: Sections of eyes recovered from horses with naturally occurring uveitis and from Shetland ponies with experimental leptospira-induced uveitis were stained by hematoxylin and eosin for histopathological evaluation. Immunohistochemistry was used to evaluate retinas for MHC Class II antigen expression and infiltration of T and B lymphocytes. RESULTS: Histopathological abnormalities in retinas from horses with uveitis ranged from minimal to total loss of retinal tissue. MHC Class II antigen-positive round and dendritiform cells were seen in these retinas, but were not seen in retinas from horses without uveitis. There was no significant reactivity noted in the retinal pigment epithelial cells or Muller cells. Numbers of MHC Class II antigen-expressing cells and T lymphocytes correlated with the extent of retinal histopathology. B lymphocytes were seen primarily in retinas from horses that were seroreactive for Leptospira interrogans serovar pomona. Retinas from ponies with experimental uveitis had changes similar to those from horses with spontaneous uveitis. CONCLUSIONS: These results suggest that retinal pathology may be a primary immunological event in equine uveitis, provide evidence that leptospira-associated uveitis may be a distinct subset of equine uveitides, underscore the relevance of the study of equine uveitis to human uveitis, and support the plausibility of a post-infectious immunopathogenesis of some naturally occurring uveitides in both humans and horses.

Association of leptospiral seroreactivity and breed with uveitis and blindness in horses: 372 cases (1986-1993).

Recurrent uveitis, a leading cause of blindness in horses, often develops as a sequela to systemic leptospirosis. Over a 7-year period, 63 of 112 (56%) horses with uveitis were seropositive for Leptospira interrogans serovar pomona, but only 23 of 260 (9%) horses without uveitis were seropositive. Odds-ratio analysis revealed that seropositive horses were 13.2 times more likely to have uveitis than were seronegative horses. Of the 63 seropositive horses with uveitis, 59% developed blindness, compared with only 24% in the 49 seronegative horses with uveitis that lost vision in 1 or both eyes during the same period. Odds-ratio analysis revealed that seropositive horses with uveitis were 4.4 times more likely to lose vision than were seronegative horses with uveitis. Of the 112 horses with uveitis, 28 (25%) were Appaloosas, compared with only 10 of the 260 (4%) horses without uveitis (odds ratio, 8.3). In addition, 19 of the 28 (68%) Appaloosas with uveitis developed blindness, compared with only 30 of the 84 (36%) non-Appaloosas with uveitis that lost vision in 1 or both eyes (odds ratio, 3.8). This field study therefore confirmed a strong positive relationship between uveitis and leptospiral seroreactivity in horses. Furthermore, the data suggested that seropositive horses with uveitis were at increased risk of losing vision, compared with that in seronegative horses with uveitis, and that Appaloosas were at increased risk of developing uveitis and associated blindness, compared with that in non-Appaloosas.

Pinealitis accompanying equine recurrent uveitis.

There is no direct verification of pineal gland involvement in human uveitis. Specimens of pineal tissue are not available during active uveitis in human patients. Naturally occurring uveitis in horses gives us an opportunity to examine tissues during active ocular inflammation. We examined the pineal gland of a horse that was killed because it had become blind during an episode of uveitis. The clinical history and histopathology of the eyes were consistent with post-leptospiral equine recurrent uveitis. The pineal gland of this horse had significant inflammatory infiltration consisting mainly of lymphocytes with some eosinophils. This observation of pinealitis accompanying equine uveitis supports the animal models of experimental autoimmune uveoretinitis with associated pinealitis and suggests that the pineal gland may be involved in some human uveitides.

Pinealitis coincident with recurrent uveitis: immunohistochemical studies.

Although experimental models of autoimmune uveitis predict pinealitis coincident with uveitis, there is no direct evidence of pineal pathology accompanying a human uveitis. Horses with naturally occurring uveitis are a potential source of eye and pineal tissues that are not available from human patients with active uveitis. We have observed pinealitis in a mare with equine recurrent uveitis. By immunohistochemistry we demonstrated immunoglobulin and MHC Class II antigen on infiltrating and resident cells of eye and pineal gland. These results support the relevance of the animal models and suggest that pinealitis may be coincident with some human uveitides.