Super-resolution immunohistochemistry study on CD4 and CD8 cells and the relation to macrophages in human cochlea.

Recently, the human cochlea has been shown to contain numerous resident macrophages under steady-state. The macrophages accumulate in the stria vascularis, among the auditory nerves, and are also spotted in the human organ of Corti. These macrophages may process antigens reaching the cochlea by invasion of pathogens and insertion of CI electrode. Thus, macrophages execute an innate, and possibly an adaptive immunity. Here, we describe the molecular markers CD4 and CD8 of T cells, macrophage markers MHCII and CD11b, as well as the microglial markers TEME119 and P2Y12, in the human cochlea. Immunohistochemistry and the advantageous super-resolution structured illumination microscopy (SR-SIM) were used in the study. CD4 and CD8 cells were found in the human cochleae. They were seen in the modiolus in a substantial number adjacent to the vessels, in the peripheral region of the Rosenthal's canal, and occasionally in the spiral ligament. While there are a surprisingly large number of macrophages in the stria vascularis as well as between the auditory neurons, CD4 and CD8 cells are hardly seen in these areas, and neither are seen in the organ of Corti. In the modiolus, macrophages, CD4 and CD8 cells appeared often in clusters. Interaction between these different cells was easily observed with SR-SIM, showing closely placed cell bodies, and the processes from macrophages reaching out and touching the lymphocytes. Otherwise the CD4 and CD8 cells in human cochlear tissue are discretely scattered. The possible roles of these immune cells are speculated.