We describe the morphological changes of the endolymphatic sac following inner ear immune reactions, and we discuss the mechanisms of endolymphatic hydrops. Hartley guinea pigs were immunized with bovine type II collagen (BIIn), Keyhole limpet hemocyanin (KLH) or horseradish peroxidase (HRP), boosters and challenging antigens were injected through the stylomastoid foramen. Animals were sacrificed every few days up to 56 days after the antigen challenge. Polyethyleneimine (PEI) was used as a cationic tracer to demonstrate the location of anionic sites on the basement membrane. In the animals immunized with BIIn or HRP, mild to moderate endolymphatic hydrops, an infiltra-tion of mononuclear cells and a significant decrease of anionic charge in the sac tissue were observed in the early postimmunization stage. However, the KLH immunization group did not show remarkable tissue changes. The blood-labyrinth barrier descriminates according to size and charge barrier may control antigen transfer and macromolecular transport into the inner ear. Immune reactions in the inner ear may lead to impairment of barrier function, hyperpermeability of the vessels and malab-sorption of endolymph, and subsequently the development of endolymphatic hydrops.
