Evaluation of eosinophilic cationic protein levels in patients with eosinophilic pneumonia

We investigated the significance of eosinophilic cationic protein (ECP) as a biological indicator of disease activity in patients with eosinophilic pneumonia (EP). ECP levels were measured in serum and bronchoalveolar lavage fluid (BALF) samples from patients with EP or other diffuse interstitial lung diseases and from healthy subjects. Also we performed immunohistochemical staining of lung tissue sections from patients with EP using anti-EG 2 antibody, and computed the correlation between the number of EG 2-positive cells in lung tissues and ECP levels in serum and BALF from patients with EP. Levels of ECP in serum and BALF samples from patients with EP were significantly elevated compared to the levels in samples from other interstitial lung-disease patients and healthy subjects. Additionally, changes in serum ECP levels reflected the clinical courses for EP patients. Approximately 90 percent of the infiltrated eosinophils in tissue sections from patients with EP were EG 2-positive and activated. The number of EG 2-positive cells in lung tissues correlated significantly with levels of ECP in serum and BALF samples from patients with EP. These findings suggested that ECP levels in serum and BALF reflect the degree of eosinophil activation in lung tissues and the degree of disease activity in patients with EP. We concluded that ECP may serve as a useful biological indicator in EP.