The eosinophilic injury to the mucosa of the airways in the pathogenesis of bronchial asthma.

Eosinophilic bronchitis and desquamation of the bronchial mucosa are the salient features of the pathology of both allergic (extrinsic) and nonallergic (intrinsic) asthma. Because of this association, the possibility of the eosinophil being the cause of the injury to the bronchial mucosa has been investigated during the last decade. In vitro, eosinophil granule major basic protein (MBP) concentrations as low as 10 micrograms.ml-1 cause desquamation and destruction of the epithelium of the airways which mimic the morphology of damage to the mucosa of the bronchi in asthma. Concentrations of MBP in the cytotoxic range for the bronchial mucosa in vitro have been measured in sputum of asthmatics (up to 92 micrograms.ml-1) and decline with treatment. Deposits of MBP have been detected by immunofluorescence within ulcerated areas of bronchial mucosa and necrotic portions of the bronchial wall in patients who had died of asthma. Most recently, the eosinophil peroxidase (EPO) and the eosinophil cationic protein (ECP) have also been found to be toxic for the epithelium of the airways in vitro, thus increasing the cytotoxic capability of the eosinophil against the bronchial mucosa in asthma. These latest research data continue to support the "eosinophil hypothesis" in the pathogenesis of this disease. According to this hypothesis, in the formidably complex network of cells and mediators responsible for the bronchial obstruction, the destruction of the mucociliary apparatus and the characteristic hyperresponsiveness of the airways in asthma; the eosinophil is the principal effector cell. In bronchial asthma a T cell modulated eosinophilic bronchitis is the primary abnormality while bronchospasm and hyperreactivity of the airways are secondary phenomena.