Bronchoalveolar lavage (BAL) was used in these studies to examine the local effects of inhalational antigen challenge on lung lavage cell populations and to determine the safety of BAL in this setting in mild asthmatic patients. For safety reasons, the timing of BAL in these studies was designed to purposefully avoid the peak airway responses to antigen challenge. We found, using strict selection criteria for subjects with bronchial asthma, that BAL performed after allergen BPC is feasible and can be a safe technique to evaluate local airway responses to antigen challenge. The BAL combined with BPC did not affect the occurrence of an early or late asthmatic response, and no fall in FEVi was induced by the lavage procedure itself.
Rankin and co-workers also found no significant decrease in FEV1 in mild asthmatic subjects undergoing BAL; however, the patients in this study were not exposed to an aerosol challenge with allergen. De-Monchy and co-workers also lavaged mild asthmatic subjects after exposure to aerosolized allergen. Although there did not appear to be any complications in this study, pulmonary function tests were not performed after the lavage to document the safety of this procedure after experimental exposure to antigen. The present studies also support the recent guidelines that were established for these types of studies by the American College of Chest Physicians, the American Academy of Allergy and Immunology, the American Thoracic Society, the National Heart, Lung and Blood Institute, and the National Institutes of Allergy and Infectious Diseases.
Prior studies by DeMonchy et alu showed that there were increased eosinophils but no neutrophils in lavage fluid of asthmatic patients after an aerosol challenge; however, no baseline studies were performed on these patients. In this regard, Godard et al showed that eosinophils were increased, at baseline, in asthmatic subjects. The present study shows that eosinophils are increased at baseline in lavage fluid of asthmatic patients and increased further with aerosol exposure to allergen. The increased numbers of neutrophils at four but not 24 hours in the present study may be explained by the fact that lavage was performed at earlier time points in the present study compared to the study by DeMonchy et al. These observations suggest that both neutrophils and eosinophils migrate into the airways within four hours of allergen challenge and are consistent with prior studies which showed an influx of neutrophils, especially at six hours, in late phase responses in the skin. In addition, both neutrophil chemotactic activity (NCA) and eosinophil chemotactic activity (ECA) have been demonstrated in peripheral blood during early and late phase responses which suggest that these cells may migrate into the airways in response to these inflammatory mediators. The present studies in asthmatic patients are also consistent with the studies of Marsh et al who showed an increase of neutrophils and eosinophils after antigen challenge in an animal model of asthma.
Electron microscopy of lavage cells from asthmatic patients demonstrated degranulation of both mast cells and eosinophils following allergen exposure. The changes in eosinophils were characterized primarily by loss of central cores and vesicle formation. These changes in eosinophils appeared to be similar whether taking place during BPC or concurrent with seasonal exposure. Both large granules, which contain major basic protein, and small granules appeared to be affected. This observation is consistent with the suggestion by Filley et al that major basic protein (MBP) may be important in the pathogenesis of asthma. In this regard, MBP has been shown to be toxic to epithelial cells of the airways. A more detailed examination of eosinophil granule dissolution was reported elsewhere.
Electron microscopy of cells obtained by lavage after BPC suggests that mast cells may be activated under these conditions in asthmatic patients to release stored and matrix mediators. The numbers of mast cells obtained were small; however, a recent study of human mast cells in BAL suggests that greater numbers are initially present in asthmatic patients compared to normal subjects. Thus, luminal mast cells may participate in early and late asthmatic responses.
Other investigators have suggested that the alveolar macrophage (AM) may be involved in asthma, and Tonnell et al have suggested that the AM in asthmatic lungs can be stimulated locally by antigen. Godard and co-workers have shown that asthmatic AM may be impaired functionally, perhaps by toxicity from the large number of eosinophils in asthmatic airways. Consistent with these observations, we have recently discovered a marked increase in macrophages staining with peroxidase which could represent newly recruited monocytes or alternatively, macrophages ingesting enzymatic products from other cells such as eosinophils (Fig 3C).
The present studies thus document the feasibility of using BAL to study local pathogenetic mechanisms in allergic bronchial asthma. The methodology appears safe in patient groups selected using the criteria and techniques described. In addition, sequential studies can be performed to evaluate changes in local pulmonary cell populations or release of mediators in response to bronchoprovocation or seasonal exposure to antigen. The inflammatory consequences of allergen exposure, increasingly recognized as resulting from late phase responses, can thus be delineated directly using techniques described here.