Immunopathology of the Inner Ear: An Update

Abstract

We have reviewed the events of an inner-ear immune response. The perilymph contains antibody, presumably derived from the systemic circulation and CSF, which would allow for neutralization and help with opsonization and complement fixation. The endolymphatic sac contains immunocompetent cells capable of processing and presenting viral or bacterial antigen, potentiating the immune response, attacking the invaders directly or attacking infected cells, and developing immunoglobulin responses in situ. The early release of mediators such as IL-2 likely emanate from the endolymphatic sac and result in potentiation and regulation of the response and may assist in changes in the SMV, including expression of ICAM-1, which aid in the egress of immune cells from the systemic circulation. PMNs arrive first, followed by T cells and B cells, with secretion of specific antibody a relatively late event. Concomitant with the increase in cellular constituents is the formation of a dense extracellular matrix. The inner ear appears to have remarkable difficulty in clearing this matrix, ultimately resulting in ossification. The immune response is unfortunately deleterious to the inner ear, resulting in degeneration of the organ of Corti, stria vascularis, and spiral ganglion. Hearing loss is consistently seen following sterile and virally induced labyrinthitis. The inner ear also appears to be a target for autoimmune disease. While inner-ear damage has been described as part of non-organ-specific autoimmune disease, specific disease against the hearing apparatus is also likely. Experimental paradigms have allowed alterations of both the afferent and efferent limbs of this response; ultimately, with the hope that we can alter the course of the response and the subsequent damage in patients.

Serial Audiometry in a Clinical Trial of AIED Treatment

“…Hearing restoration in AIED requires a therapeutic approach that effectively addresses a complex pattern of immune-mediated injury to the cochlea. AIED is thought to result from impaired surveillance mechanisms of self-tolerance and immunemediated injury (2). Loss of regulation of antibodies and activated lymphocytes produce hair cell and neuronal injury and consequent audiovestibular dysfunction.…”

Passive Transfer of Experimental Autoimmune Labyrinthitis

“…Evidence to support this includes reports which demonstrate (a) an improvement in the hearing level in patients treated with immunosuppressive drugs, (b) detection of specific cellular-and antibody-mediated immune responses in some patients, (c) coexistence of sensorineural hearing loss in several autoimmune diseases, and (d) observation of hearing loss in animal models, possibly due to an autoimmune pathogenesis [Moscicki, 1994;Harris et al, 1997;Barna and Hughes, 1997]. These studies demonstrate inflammatory and immunological changes in association with hearing loss, such as in idiopathic progressive sensorineural hearing loss, Ménière's disease and delayed endolymphatic hydrops.…”

Sensorineural hearing loss in pediatric celiac patients

“…Endolymphatic sac is producing interleukin-2 which regulates the immune response. IL-2 activation of endothelial cells of the spiral modiolar vein potentiates the intercellular adhesion molecule-1 expression which recruites more leucocytes from the bloodstream and potentiation of immune response resulted [26,27].…”