An attempt was made to elucidate the cytological nature of the defense mechanisms of the normal middle ear with special emphasis on the secretory system. Autoradiography was performed with the use of isotope-labeled glucose in order to determine the rate of glucose uptake by middle ear cells, particularly by secretory cells. Mucus-secreting glands in the guinea pig eustachian tube incorporated a large amount of glucose, while the demilune cells (serous) incorporated only a moderate amount. Some simple squamous epithelium of the bulla also took up a large amount of glucose. Since the mucous blanket of the bulla was labeled after only one hour, it is speculated that these flat cells are of the secretory type. A cytochemical demonstration of the enzyme acid phosphatase was done in order to determine the localization of this lysosomal enzyme in the middle ear cells. A strong reaction was consistently noted in the cytoplasm of both light (mucous) and dark (serous) secretory cells. This reaction appears to take place on the outer surface of the secretory granules, but, occasionally, it takes place inside the granules. The strongest reaction was noted in the lysosomal bodies. A weak reaction was frequently noted in the nuclear chromatin of the secretory cells. An immujiofluorescent study demonstrated the presence of immuuoglobulin-producing cells in the eustachian tube and in the guinea pig middle ear mucosa. Fluorescein-labeled cells (round cells) were numerous, particularly in the eustachian tube near the glands. It can be suggested from the foregoing that the middle ear is provided with mucociliary, enzymatic, and immunological (secretory and serum) defense systems. The pathological characteristics of human serous otitis were also reviewed. Evidence was shown of an increase in the number of secretory and ciliated cells, of free macrophages, and of the round cells of the submucosal connective tissue. Evidence of the free escape of transudate through intercellular spaces of the epithelial cells and capillary wall damage in the submucosal layer was also noted in pure serous effusion cases. These changes arc identical to those that take place in inflammatory reactions. The middle ear effusion, therefore, can be looked upon as the result of enhanced middle ear defense mechanisms occurring in different Phases.
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