Pulmonary eosinophils express HLA-DR in chronic eosinophilic pneumonia

Background: Chronic eosinophilic pneumonia is a rare idiopathic disorder. What role the eosinophil plays in the pathogenesis of this disease is unknown. The recent finding that mature eosinophils can express the class II major histocompatibility complex molecule HLA-DR suggests an immunologic role, perhaps through antigen presentation. The purpose of this research was to determine whether lung-derived eosinophils exhibit in vivo expression of HLA-DR. Methods: Eosinophils were obtained simultaneously from bronchoalveolar lavage and peripheral blood from a 59-year-old woman with asthma and chronic eosinophilic pneumonia. Eosinophil-enriched aliquots of peripheral blood were cocultured with human lung fibroblasts (with or without additional granulocyte-macrophage colony-stimulating factor). The percentage of cells expressing HLA-DR was quantitated by flow cytometric analysis. Results: Eosinophils derived from bronchoalveolar lavage displayed in vivo expression of HLA-DR (86%) in contrast to those from peripheral blood (7%), suggesting compartmentalization of eosinophil activation within the lung. Peripheral blood eosinophils retained the capacity for HLA-DR expression when coincubated with lung fibroblasts (83%) with augmentation by granulocyte-macrophage colony-stimulating factor (93%). Conclusion: These data demonstrate that lung eosinophil HLA-DR expression occurs in vivo; it may contribute to the pathogenesis of inflammatory lung injury.