The Distribution and Prevalence of Macrophages in the Cochlea Following Cochlear Implantation in the Human: An Immunohistochemical Study Using Anti-Iba1 Antibody

The Distribution and Prevalence of Macrophages in the Cochlea Following Cochlear Implantation in the Human: An Immunohistochemical Study Using Anti-Iba1 Antibody: Hypothesis:

Cochlear implantation may cause an increase in the number of macrophages in the human cochlea similar to previous findings in the vestibular endorgans.

Background:

Macrophages play a key role in both an inflammatory response and homeostatic maintenance. Recently, an increase in the prevalence of macrophages was demonstrated in the human vestibular endorgans after implantation. However, the prevalence of macrophages in the cochlea after implantation is unclear. The aim of this study was to compare the distribution and prevalence of macrophages in implanted human cochleae and the contralateral unimplanted ears.

Methods:

The prevalence of macrophages in the cochlea in 10 human subjects who had undergone unilateral cochlear implantation was studied by light microscopy using anti-Iba1 immunostaining. The densities of macrophages in the osseous spiral lamina (OSL) and Rosenthal's canal (RC) in implanted cochleae were compared with the contralateral unimplanted ears. The distribution of macrophage morphology (amoeboid, transitional, and ramified) was also compared.

Results:

There were activated and phagocytosing macrophages within the fibrotic sheath surrounding the electrode track and within fibrous tissue with lymphocytic infiltration in implanted ears. The densities of macrophages in OSL and RC in implanted ears were significantly greater than in unimplanted ears in some areas. There was also a difference in the prevalence of macrophage phenotype between the OSL and RC.

Conclusion:

An increase in the density of macrophages in the cochlea after cochlear implantation was demonstrated. Both phagocytosis and anti-inflammatory activity of macrophages were suggested by the distribution and prevalence of macrophages in the implanted cochlea.

Address correspondence and reprint requests to Joseph B. Nadol Jr, M.D., Department of Otolaryngology—Head and Neck Surgery, Massachusetts Eye and Ear, 243 Charles Street, Boston, MA 02114. E-mail: joseph_nadol@meei.harvard.edu

This work was supported by grants #U24-DC013983 and R01-DC000152-34 from the National Institute of Deafness and Other Communication Disorders (NIDCD).

The authors disclose no conflicts of interest.

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