The distribution of eosinophils and lymphocytes in the large and small airways of asthmatics

Airway inflammation in asthma consists of variably increased numbers of mononuclear and polymorphonuclear cells, and there is a growing body of evidence to suggest a primary role for lymphocytes and eosinophils in the pathogenesis of asthma. The aim of this study was to examine the distribution of lymphocytes and eosinophils in the bronchial tree of cases of mild and severe asthma. In cases of fatal asthma (n=10), nonfatal asthma (sudden nonrespiratory death with a history of asthma n=10), and control cases (sudden death with no history of respiratory illness, n=10), lymphocytes and eosinophils were counted in transverse sections of large and small airways stained with haematoxylin and eosin. Cases of fatal asthma had longstanding severe asthma and nonfatal cases generally had mild asthma. Lymphocytes were increased in all airway size groups both in fatal and nonfatal cases of asthma compared to control eases (p<0.001). Eosinophils were increased (p<0.001) in all airway size groups in the cases of fatal asthma compared to the nonfatal asthma and control groups, which were similar. These differences between case groups were of similar magnitude, when only a random single airway section from each case in each size group was examined, The numbers of lymphocytes correlated with the number of eosinophils in the fatal asthma group (r=0.60; p<0.0001), and to a lesser extent in the nonfatal (r=0.34; p=0.001) and control groups (r=0.32; p=0.001). These findings suggest that increased numbers of lymphocytes are uniformly distributed in the large and small airways in cases of asthma, independently of asthma severity, and that eosinophil recruitment may be related to asthma severity, Hence, biopsy specimens of the proximal airways are likely to be representative of the cellular infiltrate in large and small airways in mild and severe asthma.