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Immune Response of Macrophage Population to Cochlear Implantation: Cochlea Immune Cells
Kathryn Y Noonan1, Ivan A Lopez2, Gail Ishiyama2
1Tufts Medical Center, Boston, Massachusetts.
Insights
Cochlear implantation (CI) alters the distribution of macrophages in the human cochlea. These immune cells are present at baseline and respond to CI trauma, but their exact role requires further investigation.
Area of Science:
- Immunology
- Otolaryngology
- Cell Biology
Background:
- Macrophages are key immune cells in the cochlea, potentially influencing cochlear implant (CI) outcomes.
- Previous research suggests macrophages may phagocytize implant material and increase with surgical stress.
- The specific function and response of human cochlear macrophages to CI remain largely unknown.
Purpose of the Study:
- To investigate the inflammatory response to CI by comparing cochlear macrophages in implanted and nonimplanted human temporal bones.
- To determine the presence and distribution of ionized calcium binding adaptor 1 (Iba1) and CD68 macrophages in the human cochlea following CI.
Main Methods:
- Analysis of nineteen temporal bones: nine from implanted ears, seven from contralateral nonimplanted ears, and three from normal control ears.
- Evaluation for the presence and distribution of CD68 and Iba1 expressing macrophages using immunohistochemistry.
- Categorization of macrophage populations based on marker expression (CD68, Iba1, or both).
Main Results:
- Three macrophage populations were identified: CD68+, Iba1+, and CD68+/Iba1+ colocalizing.
- Macrophages were found ubiquitously in the cochlea, including the stria vascularis, Rosenthal canal, and spiral ganglia.
- In CI cochlea, macrophages were present around the implant path and in fibrotic areas; their density was unchanged in some cases and increased in others compared to the nonimplanted side.
Conclusions:
- Multiple macrophage populations exist in the cochlea and are present both at baseline and in response to CI trauma.
- These findings support a role for macrophages in the response to cochlear implantation.
- Further research is needed to elucidate the beneficial, detrimental, or mixed effects of these macrophages in CI patients.
Hypothesis:
The presence and distribution of ionized calcium binding adaptor 1 and CD68 macrophages in the human cochlea is altered in cochlear implantation (CI) compared with the normative or nonimplanted cochlea.
Background:
It has been hypothesized that CI induces an immunological response in macrophages leading to implant failure or reduced hearing. Macrophages are resident immune cells in human cochlea and have been shown to phagocytize implant material. In animal models, macrophage populations increase with surgical stress and with the introduction of a foreign body. However, the function and response of inner ear macrophages to CI are only beginning to be understood. This study seeks to investigate the inflammatory response to CI by comparing cochlear macrophages in implanted and nonimplanted human temporal bones.
Methods:
Nineteen temporal bones from nine implanted ears, seven contralateral controls, and three normal control ears were evaluated for the presence and distribution of CD68 and Iba1 expressing positive macrophages.
Results:
Three types of macrophage populations were detected 1) CD68 positive macrophages, 2) Iba1 positive macrophages, and 3) CD68 and Iba1 colocalizing macrophages. Macrophage distribution was ubiquitous: the stria vascularis, Rosenthal canal, and the mid-modiolus intermingled in the spiral ganglia. Iba1 and CD68 macrophages were found in the CI and non-CI contralateral and normal human cochlea. Most ionized calcium binding adaptor 1 expressing macrophages were ramified/amoeboid cells, while CD68 expressing macrophages were round shaped with foamy appearance in some areas. In the CI cochlea, both types of macrophages were detected in the fibrous sheath surrounding the CI path and within fibrotic areas within the scala tympani and the scala vestibuli in the case of CI translocation. In four cases, the density of macrophages was unchanged in the CI compared with the contralateral nonimplanted side, and in three cases, there was an increased number of macrophages in the implanted CI side compared with the nonimplanted side.
Conclusion:
Multiple populations of macrophages exist within the cochlea which are present at baseline and in response to trauma from CI. These results further support evidence for a macrophage response to cochlear implantation. Further studies are indicated to evaluate whether these macrophages have a beneficial, detrimental, or a mixed effect in CI patients.
