Immune-mediated hearing loss: basic mechanisms and options for therapy.

Immune responses are an important component of the defense of the inner ear against infection. However, immunity appears to be restricted in the labyrinth, as the inflammation associated with immune responses can damage the delicate cellular structures that mediate hearing and balance. When immunoregulation is compromised, either experimentally or through disease, immune-mediated inner ear damage and hearing loss can result. Because there are few resident leukocytes within the labyrinth, immunity and inflammation are mediated primarily by cells that enter the inner ear following the activation of post-capillary venules, which in the cochlea are the spiral modiolar veins. Activated lymphocytes are an important component of the infiltrating leukocytes, and their interactions with antigen mediate inner ear immunity. While evidence of autoimmunity specific to the inner ear is incomplete, an autoimmune origin is often suspected in idiopathic, bilateral, rapidly progressive hearing loss. Systemic immunosuppressive drugs can be effective in reversing such hearing loss, although at the cost of occasionally severe side-effects. Experimental evidence suggests that local therapy may be effective in treating this condition, if it were to target the infiltration of leukocytes into the labyrinth.