Purpose: To investigate the uveitogenic potential of retinal S-antigen (S-Ag) in horses.
Methods: Horses were immunized subcutaneously with S-Ag or BSA as control antigen, emulsified in complete Freund's adjuvant. Simultaneously, Bordetella pertussis was given intravenously. Antigen specific T- and B-cell responses were analyzed in a 3-day interval. Disease development was judged clinically and histopathologically. Two identical booster immunizations were given every 4 weeks to test induction of recurrences.
Results: T- and B-cell responses specific for S-Ag were observed in all immunized horses but were absent in control animals. However, uveitis developed in only one of five animals. Reimmunization with S-Ag did not lead to a uveitic relapse in this horse. All other horses of the S-Ag- and BSA-treated groups neither showed any signs of uveitis, nor had inflammatory infiltrates of the inner eye.
Conclusions: In contrast to interphotoreceptor retinoid-binding protein (IRBP), S-Ag is a weak autoantigen in horses. Even though S-Ag immunization leads to the activation of autoreactive T- and B-cells, infiltration of the inner eye and induction of uveitis are controlled in most horses.