BACKGROUND: The objective was to characterise the process and consequences of eosinophil activation and lysis in patients with chronic eosinophilic pneumonia and to compare them with those in patients with eosinophil pulmonary infiltrates from other causes. METHODS: Cells from bronchoalveolar lavage fluid of four patients with chronic eosinophilic pneumonia and four patients with eosinophilic infiltrates associated with Sjögren's syndrome, drug hypersensitivity pneumonia, postradiotherapy fibrosis, and pulmonary disease associated with graft versus host disease were studied ultrastructurally and with immunogold labelled antibodies directed against eosinophil proteins: major basic protein, eosinophil cationic protein, and Charcot-Leyden crystal protein. The concentration of eosinophil cationic protein was also measured in bronchoalveolar fluid. RESULTS: In the four patients with chronic eosinophilic pneumonia, ultrastructural studies demonstrated numerous lysed eosinophils. Further, three released eosinophil proteins were detected in distinct cytoplasmic structures in alveolar macrophages. These features were not found in the four patients with eosinophilic pulmonary infiltrates from other causes. CONCLUSION: Eosinophils in chronic eosinophilic pneumonia show signs of activation with release of eosinophil proteins. The appearance of three of these eosinophil proteins in different macrophage compartments suggests that macrophage uptake, with or without intracellular transport of released eosinophil proteins, involves separate mechanisms. This interaction does not lead to macrophage lysis, however, and one or more of these eosinophil proteins might directly affect macrophage function.
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