Histopathology of the airway epithelium in an experimental dual‐phase model of bronchial asthma

Abstract

Lesions of trachea cuticles are a pathological histological characteristic of bronchial asthma. Furthermore, collected tracheal cuticles desquamated from the respiratory tract are found in patients' sputum when asthma attacks occur or after the induction of allergen inhalation. From these facts, it is assumed that desquamation of trachea cuticle cells is a pathological symptom of bronchial asthma. However, there has not been any chronological report of desquamation of trachea cuticles through the process of bronchial asthma attacks. For this report, we made an experimental bronchial asthma model using guinea pigs, and conducted chronological examinations of trachea cuticle lesions related to pathological symptoms of bronchial asthma using a transmission electron microscope and a scanning electron microscope. The experimental asthma models were made by injection of ovalbumin into the abdominal cavity of guinea pigs. Then the airway responses to inhaled aerosolized ovalbumin were induced. The trachea were enucleated and examined under an optical microscope, a transmission electron microscope (hereafter abbreviated as TEM), and a scanning electron microscope (hereafter abbreviated as SEM) after 1, 2, 4, 8, 12, 24 h and 7 days after the immediate airway responses. Intercellular oedema of ciliated epithelium was observed in the sensitization groups immediately after the immediate airway response. SEM observation revealed increased mucus secretion and shortening of cilium. A slight case of desquamation or deciduation of ciliated epithelium was also beginning to appear. TEM observation revealed a dilation of ciliated epithelium intervals. Infiltration of eosinophilic leucocytes was already detectable beneath the ciliated epithelium. The degree of ciliated epithelium desquamation and infiltration of eosinophilic leucocytes progressed with time. When the late airway response occurred 4 hours later, eosinophilic leucocytes had increased drastically, and ciliate epithelium had desquamated to the extent that basal cells were exposed. Seven days after the immediate airway response, epithelium intercellular oedema had improved, and cilium had been reproduced. These results suggest that desquamation of epithelium caused by trachea cuticle lesions appears at an early stage of an asthma attack, owing to the contraction of the trachea, and that the damage is intensified by the infiltration of eosinophilic leucocytes.