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Published on: June 22, 2016
Immunologic responses in experimental cytomegalovirus labyrinthitis
J P Harris1, J T Fan, E M Keithley
1Department of Surgery, University of California Medical Centers, San Diego 92103.
Insights
Cytomegalovirus (CMV) infection causes hearing loss through immune responses, not direct viral damage. Immunosuppression improved hearing, highlighting the role of inflammation in CMV labyrinthitis.
Area of Science:
- Otolaryngology
- Virology
- Immunology
Background:
- Cytomegalovirus (CMV) labyrinthitis is a significant cause of hearing impairment.
- Understanding the precise mechanisms driving CMV-induced hearing loss is crucial for developing effective treatments.
Purpose of the Study:
- To investigate the pathogenesis of CMV labyrinthitis using a guinea pig model.
- To differentiate between direct viral cytopathic effects and host immune responses in CMV-related hearing loss.
Main Methods:
- Guinea pigs, both seronegative and seropositive for CMV, were inoculated via cardiac, perilymph, or endolymphatic sac routes.
- Immunologic, histologic, and electrophysiologic parameters were assessed.
- CMV-infected animals were immunosuppressed with cyclophosphamide to evaluate the role of immune response.
Main Results:
- Seronegative animals exhibited progressive hearing loss, inflammation, and neural degeneration.
- Endolymphatic sac inoculation led to deafness and hydrops.
- Immunosuppression significantly preserved hearing, correlating with reduced cellular infiltration, suggesting inflammation, not viral replication, is key.
Conclusions:
- Host immune responses play a critical role in the pathogenesis of CMV-induced hearing loss.
- Inflammation, rather than direct viral cytopathic effects, is the primary driver of hearing impairment in CMV labyrinthitis.
- The study underscores the importance of modulating immune responses for managing CMV-related hearing loss.
Abstract:
To better understand the pathogenesis of cytomegalovirus labyrinthitis, a guinea pig model was created. Following inoculation at several sites (cardiac, perilymph, and endolymphatic sac) in both seronegative and seropositive animals, the immunologic, histologic, and electrophysiologic responses were measured. Seronegative animals uniformly showed progressive hearing loss with marked inflammation and degeneration of neural elements. In animals inoculated into the endolymphatic sac, an associated endolymphatic hydrops developed in addition to deafness. Seropositivity protected the hearing, but endolymphatic sac inoculations resulted in mild hydrops due to local inflammation that was devoid of evidence of viral replication. The question of whether hearing loss was attributable to local inflammatory responses rather than the cytopathic effects of the virus was then examined. To test this hypothesis, animals were immunosuppressed with cyclophosphamide prior to intracochlear inoculation of cytomegalovirus. The immunosuppressed animals showed significantly better hearing than the controls, and this correlated directly with the degree of cellular infiltration of the scala tympani. These studies confirm the importance of host immune responses in the pathogenesis of hearing loss due to cytomegalovirus.
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