Immunohistochemical and immunopathologic characterization of superficial stromal immune-mediated keratitis in horses.
OBJECTIVE
To describe the immunopathologic characteristics of superficial stromal immune-mediated keratitis (IMMK) immunopathologically by characterizing cellular infiltrate in affected corneas of horses.


METHODS
10 client-owned horses with IMMK.


METHODS
Immunohistochemical staining was performed on keratectomy samples with equine antibodies against the T-cell marker CD3 and B-cell marker CD79a (10 eyes) and the T-helper cytotoxic marker CD4 and T-cell cytotoxic marker CD8 (6 eyes). Percentage of positively stained cells was scored on a scale from 0 (no cells stained) to 4 (> 75% of cells stained). Equine IgG, IgM, and IgA antibodies were used to detect corneal immunoglobulin via direct immunofluorescence (10 eyes). Serum and aqueous humor (AH) samples from 3 horses with IMMK were used to detect circulating and intraocular IgG against corneal antigens via indirect immunofluorescence on unaffected equine cornea.


RESULTS
Percentage scores (scale, 0 to 4) of cells expressing CD3 (median, 2.35 [range, 0.2 to 3.7]; mean ± SD, 2.36 ± 1.08) were significantly greater than scores of cells expressing CD79a (median, 0.55 [range, 0 to 1.5]; mean, 0.69 ± 0.72). All samples stained positively for CD4- and CD8-expressing cells, with no significant difference in scoring. All samples stained positively for IgG, IgM, and IgA. No serum or AH samples collected from horses with IMMK reacted with unaffected equine cornea.


CONCLUSIONS
Pathogenesis of superficial stromal IMMK included cell-mediated inflammation governed by both cytotoxic and helper T cells. Local immunoglobulins were present in affected corneas; however, corneal-binding immunoglobulins were not detected in the serum or AH from horses with IMMK.
Department of Clinical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, NC 27607, USA.
Diana O
DO
Pate
Alison B
AB
Clode
Thierry
T
Olivry
John M
JM
Cullen
Jacklyn H
JH
Salmon
Brian C
BC
Gilger
D000818:Animals; D001082:Aqueous Humor / Q000276:immunology*; D005260:Female; D006734:Horse Diseases / Q000276:immunology* / Q000473:pathology; D006736:Horses; D007070:Immunoglobulin A / Q000032:analysis*; D007074:Immunoglobulin G / Q000032:analysis*; D007075:Immunoglobulin M / Q000032:analysis*; D007150:Immunohistochemistry / Q000662:veterinary; D007634:Keratitis / Q000276:immunology / Q000473:pathology / Q000601:surgery / Q000662:veterinary*; D008297:Male; D018709:Statistics, Nonparametric
D007070:Immunoglobulin A; D007074:Immunoglobulin G; D007075:Immunoglobulin M