Role of eosinophils and lymphocytes in the pathogenesis of bronchial asthma

: Lymphocytes and eosinophils are the two major inflammatory cells in the airways of patients with asthma. We studied the phenotypic composition and activation status of eosinophils and lymphocytes in bronchial biopsies obtained from asymptomatic and symptomatic asthmatics and nonasthmatic controls. The number of EG2-positive cells (activated eosinophils), CD3- and CD4-positive cells, and CD25-positive cells (activated lymphocytes) were significantly increased in the symptomatic asthmatics. In addition, significant correlations were noted between the density of CD4- and CD25-positive cells and the degree of eosinophil infiltration and activation. These data suggest that activated eosinophils and lymphocytes are involved in the pathogenesis of asthma and that activated helper T-lymphocytes play a central role in eosinophil infiltration and activation in the airways of asthmatics. Recently, eosinophil infiltration has been though to induce airway hyperresponsiveness by damaging airway epithelium through eosinophil granule proteins. To test this hypothesis, we investigated whether the number of clusters of desquamated respiratory epithelial cells in sputum is related to the eosinophil granule proteins in sputum and whether the ultrastructural changes in the bronchial epithelium are related to the presence of eosinophils in the bronchial mucosa. The results of both studies supported the hypothesis.