Immunopathology of the Inner Ear: An Update

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.