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

Abstract

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.

Keywords: CD4; CD8; Human cochlea; Lymphocyte; Macrophage; T cell.

Fig. 1

MHCII- and CD11b-immunohistochemistry of macrophages in the human spiral ganglion. In A), variously shaped macrophages are between the spiral ganglion neurons (SGN). Both MHCII and CD11b were expressed in the macrophages. In B), an enlarged cell expressed both markers with CD11b more on the surface (arrow).

Fig. 2

IBA1-and CD8-immunohistochemistry of human cochlear modiolus. A), B) and C) show patterns of interaction between the IBA1+ macrophages and the CD8⁺ T cytotoxic cells. These images were taken either around the modiolar vessels or in the peripheral regions of the Rosenthal canal. The nuclei of the macrophages are not included in the images except for A) where the nuclei with IBA1-labeling (*) are shown close to a CD8⁺ cell. In D) a blood vessel is seen to be surrounded by several CD8⁺ T cells, note the one on the right (*) that flattens against the outer vessel wall. The other CD8⁺ cells (** and ***) appear round-shaped and at a distance from the vessel. One CD8⁺ cell (***) is enlarged and shown in B).

Fig. 3

CX3CR1-and CX3CL1-immunohistochemistry of human spiral ganglion (A) and CD4⁻, CD8⁻and IBA1-immunohistochemistry of human cochlear modiolus (B and C). In A), spiral ganglion neurons (SGN) express CX3CL1 (Fractalkine) more intense in their perikaryon surface. The receptor CX3CR1-immunostaining appears diffuse in the cytoplasm of both cell bodies (Mɸ) and processes that look like macrophages. B shows several immune cells located along the wall of scala tympani in the modiolus. Two cells positive for CD4 and CD8 respectively are magnified in B); super-resolution SIM microscopy reveals a close relation between these two cells.