chapter  14
Interactions Between Eosinophils and the Airway Epithelium
Pages 24

Eosinophils are strongly implicated in the process of epithelial injury in asthma. Elevated numbers of these cells are found in the blood and sputum of patients with the disease, and eosinophils that are apparently activated are found in the bronchial epithelium and in bronchoalveolar lavage fluid (8). Their ability to release potentially cytotoxic mediators such as oxidants and the granulederived major basic and cationic proteins, together with evidence for the abnor-

mal presence of these agents in the airway lumen in asthma {9,10), supports an association between the eosinophil and epithelial trauma. However, their probable involvement in the disease is now recognized to be a heterogeneous one. Disease symptoms sometimes occur without obvious changes in the number of eosinophils present at various sampling sites, and sometimes upregulated populations of eosinophils are seen in the airway mucosa and submucosa in the apparent absence of "clinical" asthma (8). These paradoxes are important reminders that asthma is a very complex disease (or perhaps more correctly a spectrum of disease processes) and that the biological characteristics of the eosinophil are still poorly understood. There is also increasing evidence that it is inappropriate to regard the inflammatory events in the asthmatic airway as due to the infiltrating leukocyte population alone. More complex interrelationships undoubtedly exist between infiltrating and resident cells through a cross-talk involving cytokines and other means of intercellular communication. Although clinical investigations, particularly those involving lavage and biopsy techniques, have been important in describing the possible role of the eosinophil and its interactions in the airway mucosa {11,12), studies of this type can yield little information about the mechanisms involved in such complex interactions. It is necessary to have as full an appreciation of these mechanisms as possible if we are to aspire to the dual aims of understanding the role of the eosinophil and devising more effective therapies for the disease. Attainment of these objectives therefore requires the use of in vitro models in clever combination with directed clinical investigations.