MECHANISMS OF ACUTE EOSINOPHILIC INFLAMMATION IN A CASE OF ACUTE EOSINOPHILIC PNEUMONIA IN A 14-YEAR-OLD GIRL

Background. Acute eosinophilic pneumonia (AEP) is characterized by res piratory distress, eosinophilic infiltration in the lung, acute onset, resolution of symptoms with corticosteroids and the absence of relaps e. Studies to identify the pathophysiology of AEP in adults have demon strated eosinophil activation in the BAL fluid, and the presence of hi gh levels of interleukin 5 (IL-5) in the BAL. Objective. To investigat e the pathophysiology of AEP with pleural effusion in a paediatric pat ient. Methods. ECP levels in the BAL and pleural fluid was determined by radioimmunoassay. IL-5 and GM-CSF concentrations in the BAL and ple ural fluid were measured by Elisa. Immunohistochemistry studies perfor med on open lung biopsy included a specific ICAM-1 immunostaining and a ECP specific immunostaining (EG2(+)). Results. High levels of ECP we re found in the BAL (5 mu g/L) and pleural fluid (750 mu g/L) demonstr ating eosinophil activation at these sites. Immunohistochemistry illus trated activated (EG2(+)) eosinophils in the interalveolar septa and a lveolar space and detected increased expression of ICAM-1 on alveolar epithelial cells. High levels of IL-5 were measured in the BAL (1334 p g/mL) and pleural fluid (7014 pg/mL), while elevated concentrations of GM-CSF (150 pg/mL) were found in the BAL. Conclusion. We conclude tha t in this paediatric patient with AEP activated eosinophils were prese nt in the BAL fluid, in the interalveolar septa and in the pleural spa ce while increased ICAM-1 expression was detected on alveolar epitheli al cells, contributing, at least partly, for their adhesive interactio ns. IL-5 and GM-CSF are likely important to the massive eosinophil rec ruitment and activation in the lung, while IL-5 is probably related to eosinophil accumulation and activation in the pleural space. Thus, lu ng generation of eosinophil-active cytokines is central to the pathoph ysiology of AEP in paediatric patients.