Since Rask-Andersen and Stahle reported the existence of macrophages and lymphocytes in the endolymphatic sac in 1979, the endolymphatic sac has been thought to play an important role in inner ear immune reactions. However, in the inner ear, especially in the cochlea, the first defensive mechanism in which macrophages and natural killer cells play a significant role before specific immune reactions start remain unknown. As asialoGM1 is one of the surface markers of cells with natural killer activity as well as macrophages in mice and rats, we investigated the localization of asialoGM1-positive cells in murine cochlea using immunohistochemical techniques. As a result, only a few asialoGM1-positive cells were recognized on the wall of the scala tympani by light microscopy, and transmission electron microscopy revealed that these asialoGM1-positive cells were macrophages. These cells appeared to be round or flat, and were scattered primarily at the basal turn of the cochlea and near the collecting venule. This result suggests that these cells play a defensive role against pathogens entering the cochlea, but its function is not very powerful.
