EFFECT OF ENDOTOXIN ON CULTURED RAT MIDDLE-EAR EPITHELIUM, RAT MEATALEPIDERMIS, AND HUMAN KERATINOCYTES

Several factors seem to contribute to the series of events in the path ogenesis of otitis media and cholesteatoma. Endotoxin is likely to be one of these factors, since it has been found in human middle ear effu sions and since injection of this substance into the middle ear, in an imal experiments, gave rise to prominent reactions. Provoking of epith elial cells in vitro with endotoxin led to distinct cell responses tha t might be associated with cholesteatoma formation. In this study the effect of endotoxin on serially cultured rat middle ear epithelium, ra t meatal epidermis, and human keratinocytes was investigated. Endotoxi n strongly stimulated the proliferation of middle ear epithelium and h uman keratinocytes and inhibited that of meatal epidermis. Furthermore , endotoxin affected the morphology of the three types of tissue. Rat middle ear epithelium revealed epithelial cell tracks with interconnec ting bridge-like structures protruding above the culture plane, wherea s rat meatal epidermis showed increased terminal differentiation expre ssing large areas of blister-like structures detaching from the cultur e dish. Cross-linked envelope analysis of human keratinocytes showed a n increased terminal differentiation that was morphologically confirme d but was not confirmed by cytokeratin analysis. The results of this s tudy support the hypothesis that endotoxin may play an important role in the pathogenesis of otitis media and cholesteatoma.