Functional morphology of the mucosa of the middle ear and Eustachian tube.

A review of available histological, histochemical and ultrastructural data on middle ear mucosa and the Eustachian tube was made to provide a broad cellular basis for understanding middle ear effusions. The presence of mucociliary defense system in a large part of the Eustachian tube and middle ear is seen as the first line of defense. Secretion by the mucosa has a profound biological significance. Immunoglobulins A, G, and even E and M are produced locally by the mucosa and may contribute to the immunodefense of the middle ear. Secretory lysozyme is also produced by the mucosa and may contribute enzymatic defense of the ear. Mucosal immunoglobulins and lysozyme are significantly elevated in the effusions, which would imply that local defense systems are hyperactive in OME. It also appears that these increases are related to the increase of the secretory cell population. It is also suspected that auditory surface-active agent is produced locally and may facilitate normal function of the tube. The middle ear also can transport macromolecules very rapidly across intact mucosal epithelium. The large numbers of tissue and wandering macrophages found in the mucosa and effusions would also imply that the middle ear is capable of efficient phagocytosis, which may be involved in processing antigen.