Immune mechanism has been postulated as one of the possible pathoetiology for Meniere's disease, since it is clinically well known that some patients with Meniere's disease show remarkable recovery from fluctuated and repeated sensorineural hearing loss or vertigo by systemic application of corticosteroid. However, there still has been a distance between the clinical entity and the basic knowledge of anatomy and immunology obtained so far. Moreover, little is known about bone marrow-derived cells or immune-competent cells in the vestibule on the basis of experimental research. In this study, we studied the distribution and phenotypes of bone marrow-derived cells in the vestibule using bone marrow-chimeric mice, in which bone marrowderived cells were visualized with green fluorescence.
In order to make bone marrow-chimeric mice, bone marrow was obtained from GFP mice with green fluorescence expressed in every cell in the body. Adult C57 BI/6 mice received systemic irradiation to ablate their own bone marrow, and then were systemically applied bone marrow derived from GFP mice. Three month after bone marrow transplantation, the inner ears were collected and processed for cryostat sections. The specimens were studied with a fluorescent microscope.
In the endolymphatic sac, bone marrow-derived cell were found in the epithelial layer and lumen of the sac, as previously reported, and most of these cells exhibited the phenotype of macrophage. In contrast, bone marrow-derived cells were observed being limited within the stroma in the vestibular ganglion or underneath the sensory epithelia of the utricle, saccule, and ampullae of semicircular canals. Immunohistochemical study demonstrated that more than 70% of bone marrow-derived cells in the vestibule showed the phenotype of macrophage.
These results proved that bone marrow-derived cells exist mainly as vestibular macrophages in the stroma underneath the vestibular sensory epithelia, even when without damage. It is also indicated that the vestibular macrophages appeared to be novel constitutive cells in the vestibule, and would have a potential to be a therapeutic target in vestibular disorders.
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