Effects of tobacco on the ear

Squamous metaplasia of the middle ear epithelium

This study deals with the expression of cytokeratins (Cks) in squamous cell metaplastic lesions in rat and human middle ear. In rats, squamous metaplastic lesions could be induced during chronic otitis media. The histological features of these lesions were similar to those observed in the human middle ear. Immunohistochemistry revealed that squamous cell metaplasia in both rat and human middle ear is characterised by a loss of simple epithelial cell related Cks and the appearance of Cks characteristic of stratified and cornifying epithelia. This indicates a true change in the differentiation of the middle ear epithelium. It is concluded that the Ck profile of the cholesteatoma matrix cannot be used as a variable to decide whether the origin of cholesteatomas is epidermal or metaplastic. This rat model is suitable for studying squamous cell metaplasia in relation to cholesteatoma genesis.

The effect of external stimuli on rat middle ear epithelium in culture. Extracellular carbon dioxide concentration

Serially cultivated rat middle ear epithelium was studied under exposure to various concentrations of carbon dioxide. Three experiments were performed exposing the epithelium to a gaseous environment containing 5 or 10% CO2 or to an atmosphere almost devoid of CO2. Oxygen was maintained constant at 20% and nitrogen was additionally supplied. Cells exposed at 0% CO2 showed a remarkably different morphology compared with the cultures at 5 and 10% CO2, cells could become extremely large at 0% CO2, also showing a great variation in shape and cell size within the culture. Proliferation was significantly impaired at 0% CO2 vis-à-vis the 5 and 10% experiments. Terminal differentiation, however, was not influenced by the different CO2 concentrations, indicating that in vitro, variation in CO2 concentration is of no importance regarding a possible differentiation of middle ear epithelium into a cornifying epithelium.

Squamous metaplasia of the middle ear mucosa during vitamin A deprivation

Adult and juvenile albino rats were maintained on a vitamin A-free test diet for 2 to 28 weeks. Histologic study of the middle ear and eustachian tube mucosa of these animals showed extensive focal squamous metaplasia when compared with the control group. Keratinization of large areas of normally columnar, ciliated epithelium was observed without frank keratoma formation. In over half of the most vitamin A-deficient animals, acute otitis media with effusion was found. It is hypothesized that vitamin A deficiency disrupts the mucocilliary clearing mechanism in the middle ear and eustachian tube, which may lead to effusion and otitis media.

Effect of environmental CO2, O2 and pH on the growth of respiratory epithelium in vitro

Explants of rabbit tracheal epithelium were exposed to various CO2 and O2 levels and to different pH values for two weeks in organ culture. During culture the original explanted epithelium gradually changed from pseudostratified to stratified and there was a decrease in goblet cell density, and in the amount of PAS positive material in these cells. The changes in stratification were found to be independent of the pH of the medium or the CO2 level, but the proportions of ciliated cells and goblet cells were affected by the CO2/O2 ratio and by pH. Coordinated ciliary activity was preserved in most explants except for those cultured at high (80 and 95%) oxygen levels. A new growth of epithelium gradually covered the exposed connective tissue. This new epithelial growth developed the phenotypic expression of the original tissue; it gradually differentiated into ciliated cells and goblet cells. At increased CO2 levels and a high pH (7.7), differentiation into goblet cells increased fourfold, while differentiation into ciliated cells decreased. These findings suggest that high CO2 levels promote goblet cell differentiation. and thus increase the propensity for mucus secretion in unaerated epithelia. The correlation of these results with the fact that increased CO2 level present in the middle ear of patients with secretory otitis media may help to explain the large increase in the population of mucus-secreting cells in this disease process.

Tissue culture of human adult adenoids and of middle eear mucosa

The increased number of mucus producing cells as well as the presence of stratified squamous epithelium in pathological and experimental middle ear conditions, point towards the possibility of metaplastic changes of the middle ear mucosa, similar to the metaplastic capabilities of respiratory mucosae in general, as observed clinically or provoked experimentally. The purpose of this study was to develop a model of postembryonic human respiratory mucosae, in vitro, for the study of triggering or inducing factors involved in its normal and metaplastic differentiation. Explants from adenoids and middle ear mucosa were cultured, both as organ cultures and monolayers, for periods of up to two weeks, and their developmental characteristics were studied and described. Over 50% of the explants showed mitosis, epithelial and monolayer growth, ciliary activity and differentiation into ciliated and into mucus-producing cells. Adenoid explants were grown in air without and with added 5% CO2. Under the latter conditions, the proportion of explants and monolayers showing ciliary activity was 50% greater. It is concluded that this model might be suitable for further studies of the factors which control cyto-differentiation in mucociliary epithelia. Maintaining its growth for a longer period would, however, be desirable.

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.

Functional morphology of the lining membrane of the middle ear and Eustachian tube: an overview

A large part of normal middle ear cavity and Eustachian tube is provided with a mucociliary transportation system which is considered the first line of defense of the middle ear. Secretory cells of the normal mucosa of the middle ear and the tube can be classified into three main types: mucous, mixed and dark granulated (or serous). This may mean that the secreta of the mucosa is biochemically diverse and/or in a dynamic state. The presence of immunoglobulin-producing plasma cells (IgA, IgG and IgM) and macrophages in the Eustachian tube and the middle ear mucosa supports the concept that the middle ear is protected by an immunologic defense system. Normal mucosal epithelial cells of the middle ear and the tube possess the ability to transport macromolecules by intact epithelial cells toward connective tissue layer where the macromolecules are either phagocytized by histiocytes or enter into capillary system. The macrophages of regional lymph nodes also picked up the macromolecules. Demonstration of lamellar substances similar to phospholipids in the secreta of the tube and middle ear mucosa of the guinea pig suggests the presence of auditory surface-active agent(s) (surfactant). Close association between secretory cells of the mucosa and acid phosphatase is demonstrated by cytochemical method. It is suggested that secretory enzymes such as lysozyme and acid phosphatase may be either produced or transported by secretory cells of the middle ear mucosa. These enzyme secretions are considered a part of the enzymatic defense system of the middle ear.

The biopathology of secretory otitis media

Recent investigations have identified the viscous middle ear effusions in secretory otitis media as being of the same nature as true mucus — the “backbone” of which is glycoproteins. The source of the mucus are mucus producing cells found in the normal middle ear lining and producing excessive amounts of mucus in pathological states. The nature of the pathological state which leads to excessive mucus production is an inflammation associated with deficient ventilation of the middle ear. Ventilation deficiency of the middle ear is a pathophysiological phenomenon which is not associated with hermetic blockage of the Eustachian tube. The “ex-vacuo” theory which assumes the tube to be blocked — the effusion to be a proteinous transudate and the middle ear devoid of mucus secreting elements, is no more tenable. Middle ear effusions can be approached by looking at them as questions of: 1) mucus clearance; 2) excessive mucus production; 3) middle ear ventilation and 4) etiology of middle ear inflammation. Clearance of mucus from the middle ear is governed by the mucociliary system, where the number of cilia and specificity of mucus are known today to be critical for clearance. Excessive amounts of mucus are secondary in the middle ear, as in all other mucosa in the body, to a metaplastic process. Mucosal stem cells can differentiate into mucus cells, ciliated cells, and keratin producing cells. In the presence of inflammation, especially when oxygen tension is low (and CO2 tension is high) mucosal stem cells differentiate into numerous mucus producing cells which have been shown, in the middle ear, to be responsible for the excessive mucus production. The nature of the mechanism of middle ear ventilation in health and disease is not yet known, though it is in all probability related to the function of the Eustachian tube muscles.