Activation of lymphocytes and increased interleukin-5 levels in bronchoalveolar lavage fluid in acute eosinophilic pneumonia.

Acute eosinophilic pneumonia (AEP) is a recently described illness and the number of case reports has increased during the last few years. However, the role of interleukin (IL)-5 and activated lymphocytes in the pathogenesis or activity of AEP is still not clear. The clinical features, lymphocyte surface analysis and IL-5 concentrations in bronchoalveolar lavage fluid (BALF) and peripheral blood (PB) of a young female patient with AEP are described before and at 2 weeks, 4 weeks and 6 months after a 3-day course of i.v. methylprednisolone. Serum and BALF concentrations of IL-5 before treatment were 5,200 and 8,400 pg x mL(-1), respectively. Activated CD4 lymphocytes bearing CD25 and human leukocyte antigen (HLA)-DR in BALF were higher than in PB. Treatment caused a rapid fall in these cells and levels of IL-5 in BALF returned to normal levels in parallel with clinical improvement. There was no evidence of recurrence after cessation of steroid therapy. In contrast, eosinophilia in BALF persisted for 4 weeks after steroid therapy in spite of normalization of the chest radiograph and arterial blood gases. The number of CD8+CD11b- (suppressor/cytotoxic) T-cells subsequently increased while the number of CD8+CD11b+ cells decreased. These results suggest that activated CD4 cells and interleukin-5 elevation contribute to the development of acute eosinophilic pneumonia rather than persistent eosinophilia in the lung and that a short course of steroid therapy may effectively control acute eosinophilic pneumonia.