TUNEL-positive labeling in mouse inner ear caused by tubulin immunization is not apoptosis

Apoptosis is involved in all fundamental processes of the immune system. To study whether apoptosis plays any role in the pathogenesis of autoimmune inner ear disease, we immunized Balb/c mice with tubulin. The inner ears were examined with TUNEL (in situ terminal dUTP nick-end labeling) and immunocytochemistry of the apoptosis regulatory proteins Bcl-2 and Bax. TUNEL-positive cells are found in the tubulin-immunized inner ears but not in the control inner ears. The positive cells are the marginal cells in the stria vascularis, and the hair cells in Corti's organ and the saccule. However, under morphological analysis by light microscope, these cells lack the features characteristic of apoptosis. Moreover, no cells staining positive for Bcl-2 and Bax are found in any structures of the inner ears. These results suggest that positive TUNEL staining in this model does not indicate apoptosis and apoptosis may be not involved in autoimmune inner ear disease.