High concentrations of eosinophil cationic protein and eosinophil protein X in eosinophilic pleural effusions

To analyze the association of the eosinophil granulocyte with pleural effusions, we measured the concentrations of two eosinophil proteins, eosinophil cationic protein (ECP) and eosinophil protein X (EPX), in pleural fluid and serum of 92 patients with pleural effusions of various causes. We observed significantly higher ECP and EPX concentrations in eosinophilic than in noneosinophilic pleural effusions (p < 0.001 and p < 0.05, respectively) and a positive correlation between the concentrations of both eosinophil proteins in pleural fluid and the total number of eosinophils in pleural fluid (ECP: r = 0.66, p < 0.0001; and EPX: r = 0.62, p < 0.0001). There was a positive correlation between the concentrations of ECP in pleural fluid and serum (r = 0.74, p < 0.0001) and between the concentrations of EPX in pleural fluid and serum (r = 0.41, p < 0.001). High ECP and EPX concentrations in pleural fluid indicated nonspecific etiology and not tuberculosis as the cause of the effusion. Our results suggest that eosinophils in pleural effusions release eosinophil proteins and probably actively participate in the local inflammatory reaction.