Immune response of the endolymphatic sac to horseradish peroxidase: immunologic route from the middle ear to the inner ear.

Twenty guinea pigs were immunized with horseradish peroxidase (HRP) intradermally and challenged with 5 mg of the same antigen in the tympanic bulla. The appearance of immunoglobulin-producing cells (plasma cells) in the inner ear structure was examined immunohistochemically in frozen sections. Four to 10 days following antigen challenge, 5 of the 20 animals showed significantly increased plasma cells in the subepithelial connective tissue of the endolymphatic sac (ES). Those cells showed positive reactions, mainly with IgG followed by IgM. The cells that reacted positively with IgA were few. Some of these plasma cells were considered to contain the specific antibody against HRP. The results indicate the role of the ES as a local immune response region for the inner ear complex, as well as the existence of an immunologic route from the middle ear cavity to the inner ear, particularly to the ES.