Increased interleukin-5 levels in bronchoalveolar lavage fluid is a major factor for eosinophil accumulation in acute eosinophilic pneumonia.

Background: Increased interleukin-5 (IL-5) levels have been reported in bronchoalveolar lavage fluid (BALF) from patients with acute eosinophilic pneumonia (AEP); however, it still remains to be determined whether IL-5 is responsible for the eosinophil accumulation in the lung.

Objective: We examined the effect of antibodies against cytokines on eosinophil chemotaxis induced by BALF from AEP patients to identify factors responsible for eosinophil accumulation.

Methods: We measured a series of specific cytokines, including IL-3, IL-4, IL-5, IL-6, IL-8, GM-CSF, RANTES, MCP-1, MIP-1alpha and eotaxin, in the BALF from 4 patients with AEP. BALF from 4 patients with chronic eosinophilic pneumonia (CEP) and 13 patients with non-eosinophilic interstitial lung diseases (ILD) were examined as controls. The eosinophil chemotactic activity in the BALF was examined using tissue culture insert furnished with a polycarbonate membrane.

Results: The total protein content in BALF from patients with AEP was extremely elevated. Even after standardization with protein concentration, IL-5 levels in AEP patients were significantly higher than those in CEP and ILD. IL-3 and chemokines were rather lower in the AEP group than in the CEP and ILD groups. In AEP BALF, anti-IL-5 neutralizing antibody significantly inhibited eosinophil chemotaxis. Antibodies against IL-3, GM-CSF, and IL-8 did not affect the eosinophil migration.

Conclusion: These findings suggest that locally produced IL-5 plays an important role in eosinophil accumulation of AEP.