Predominant Implication of IL-5 in Acute Eosinophilic Pneumonia: Comparison with Chronic Eosinophilic Pneumonia

<b>Background: </b>Acute eosinophilic pneumonia (AEP) is a rare disease with unknown etiology. To examine pathophysiology of AEP we measured the cell number of eosinophils and eosinophil active cytokines in the peripheral blood and bronchoalveolar lavage fluid (BALF) of AEP patients and compared the levels with those measured in chronic eosinophilic pneumonia (CEP) patients. <b>Methods: </b>Cell number of eosinophils in peripheral blood and BALF from patients with AEP (n = 3) and CEP (n = 3) were measured. Eosinophil active cytokines in serum and BALF from the patients were measured using ELISA. <b>Results:</b> Eosinophil cell number in peripheral blood was 274–1,377/mm³ in AEP and 526–2,500/mm³ in CEP. The percentages of BALF eosinophils were high in AEP and CEP. Eosinophilia disappeared after methylprednisolone pulse therapy (1 g for 3 days) in AEP, however the cell number of eosinophils gradually increased after methylprednisolone pulse therapy and then spontaneously decreased to within normal range without any further medication. The concentrations of IL-5 in AEP were very high in serum and in BALF, however the concentrations in CEP were low in serum and BALF. <b>Conclusion: </b>AEP is a disease in which eosinophil active cytokine IL-5 is predominantly involved; CEP is not. The factors involving eosinophil infiltration to inflammatory loci differ between AEP and CEP.