Mast cells, atypical lymphocytes, and neutrophils in bronchoalveolar lavage in extrinsic allergic alveolitis. Comparison with other interstitial lung diseases

Bronchoalveolar lavage (BAL) samples from exposed patients with extrinsic allergic alveolitis (EAA) contained mast cells in increased numbers in addition to lymphocytes. The counts rarely exceeded 0.5% in sarcoidosis, cryptogenic fibrosing alveolitis, or asbestosis or in control samples, but they were as much as 10-fold higher in EAA (p less than 0.001). Higher concentrations of histamine were demonstrated in EAA BAL-cell lysates, and histamine was released from cells challenged with anti-IgE. Electron microscopic examination confirmed that the cells were mast cells that differed from mast cells in dermal connective tissue and alveolar interstitial tissue but resembled bronchial subepithelial tissue mast cells in showing more features suggestive of activation. However, they showed more marked degranulation, and many were young. By light microscopy, they also resembled "mucosal" rather than "connective" tissue mast cells since granule staining was prevented by formaldehyde. Mast cell counts fell to normal after removal of patients from exposure, but lymphocyte increases, including atypical "blast" forms, persisted despite clinical recovery. Neutrophils were also increased before, but rarely after, removal. We suggest that EAA may provide an example of a human disease to support recent evidence that some delayed hypersensitivity disorders involve mast cells as well as lymphocytes.