Middle ear mucosa changes following exposure to Pseudomonas aeruginosa exotoxin A

Abstract

Pseudomonas aeruginosa exotoxin A (1 μg/¶20 μl) was instilled into the middle ear cavity in the rat. Morphological changes of the mucosa were analyzed after various intervals using light (LM) and transmission electron microscopy (TEM). An inflammatory cell reaction was seen in which there was a predominance of polymorphonuclear leukocytes (PMNs) and mononuclear cells that were mostly lymphocytes and monocytes/macrophages. Epithelial cells often showed signs of metaplasia and hyperplasia, followed by degradation through necrosis and/¶or apoptosis, resulting in denudation of the submucosal layer. A characteristic feature was the physical interaction between intraepithelial lymphocytes and epithelial cells. Lymphocytes adhering to the cell coat of epithelial cells showed signs of directed secretion that seemed to end in necrosis or apoptosis of the target cell. These changes occurred simultaneously with phagocytosis of cells and cell debris by PMNs and macrophages. Ultrastructural analysis suggested that intraepithelial, lymphocyte-mediated cytolysis and apoptosis may be important events in degradation of the epithelium following exposure to Pseudomonas sp. exotoxin. These findings indicate that denuding of the lamina propria may facilitate the penetration of toxin into the labyrinth, thus explaining subsequent inner ear damage.