Distribution of bone marrow-derived cells in the vestibular end organs and the endolymphatic sac

Conclusion: Bone marrow-derived cells (BMDCs) are constitutively present in the vestibular end organs and in the endolymphatic sac, and may play a role in the maintenance of inner ear homeostasis. Objectives: The aim was to examine the distribution and characteristics of BMDCs in the vestibular end organs and in the endolymphatic sac. Methods: Bone marrow-chimeric mice were generated by bone marrow transplantation from mice genetically labeled with enhanced green fluorescent protein to C57 Bl/6 mice to visualize BMDCs. Three months after bone marrow transplantation, inner ear specimens were processed for histochemical analyses. Results: BMDCs were widely distributed in the vestibular end organs and the endolymphatic sac, whereas there were differences in the phenotype and the distribution between the vestibular end organs and the endolymphatic sac. A subpopulation of BMDCs in the vestibular end organs expressed antigen-presenting protein MHC class II. Moreover, the density of BMDCs in the vestibular end organs increased in response to local mechanical stress.