Retinal immunopathology in horses with uveitis

Area of Science:

• Veterinary Ophthalmology
• Immunopathology
• Comparative Medicine

Background:

• Equine uveitis, a spontaneous disorder in horses, serves as a model for human uveitis.
• While often presenting as anterior uveitis, retinal involvement is observed in some equine cases.
• This study investigates the immunohistopathology of retinas in horses affected by uveitis.

Purpose of the Study:

• To characterize retinal pathology in equine uveitis using immunohistopathology.
• To investigate the role of immune cells and MHC Class II antigen expression in the equine retina during uveitis.
• To compare spontaneous equine uveitis with experimental leptospira-induced uveitis.

Main Methods:

• Histopathological evaluation of retinal sections from horses with naturally occurring and experimentally induced uveitis using hematoxylin and eosin staining.
• Immunohistochemistry to detect MHC Class II antigen expression and lymphocyte infiltration (T and B cells).
• Analysis of retinal tissue from healthy horses and Shetland ponies for comparison.

Main Results:

• Retinal abnormalities in equine uveitis ranged from mild to severe tissue loss.
• MHC Class II antigen-positive cells were present in affected retinas but absent in controls.
• Numbers of MHC Class II antigen-expressing cells and T lymphocytes correlated with histopathological severity.
• B lymphocytes were predominantly found in retinas of horses with leptospira-associated uveitis.
• Experimental leptospira-induced uveitis in ponies showed similar retinal changes to spontaneous equine uveitis.

Conclusions:

• Retinal pathology in equine uveitis appears to be a primary immunological event.
• Leptospira-associated uveitis represents a distinct subset of equine uveitides.
• Findings underscore the relevance of equine uveitis research to human uveitis.
• Supports a post-infectious immunopathogenesis for some uveitides in both species.