The epithelium of the human endolymphatic sac: immunohistochemical characterization

A panel of monoclonal and polyclonal antibodies has been used to study the epithelium of the extraosseous part of the human endolymphatic sac (ES) by immunohistochemistry. The ES epithelium reacted with several epithelial markers such as Lu-5, different anticytokeratins, antiepithelial membrane antigen, and anticarcinoembryonic antigen. Unexpectedly, all epithelial cells also revealed a strong positive reaction for the mesenchymal marker vimentin and for S-100 protein. 'Neuroendocrine', a neurosecretory antigen, and neuron-specific enolase reactivity was detected in a few epithelial cells. The results support the assumption that the ES epithelium is metabolically active and capable of secretion and resorption. These findings are in keeping with results of functional experiments in animals. The demonstration of neurosecretory antigen and neuron-specific enolase in some cells indicate that the epithelium may also have paracrine functions.