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.