Serum eosinophil cationic protein, eosinophil protein X and eosinophil peroxidase in relation to pulmonary function in cystic fibrosis

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Abstract
Background Recently, increased serum levels of eosinophil cationic protein (ECP) in cystic fibrosis (CF) have been reported which were closely related to the levels in sputum. In the present study we investigated other eosinophil proteins such as eosinophil peroxidase (EPO) and eosinophil protein X (EPX) in sera of patients with CF and their relation to pulmonary function. Methods Serum samples from 42 patients with CF and from 25 healthy control subjects were measured for ECP, EPO and EPX. Lung function tests were performed by using whole body plethysmographic technique, and the results were correlated with the levels of eosinophil granule proteins. Results Serum ECP (median: 20.9 μg/L), EPO (median: 30.3 μg/L) and EPX (median: 37.9 μg/L) levels were significantly increased in CF compared with healthy controls (3.5 μg/L, P < 0.0001, 5.6 μg/L, P < 0.0001 and 14.6 μg/L, P < 0.0001, respectively) whereas eosinophil counts were not different. There was a strong correlation between the levels of eosinophil proteins and variables of pulmonary function, like between ECP and forced vital capacity (r = − 0.764, P < 0.0001). In addition, ECP concentrations were significantly related to the levels of EPO and EPX, albeit, in some patients with low ECP levels, increased EPO and EPX concentrations were observed. Conclusion These results indicate that in patients with CF, ECP, EPO and EPX concentrations also were increased with a significant relationship between these three eosinophil proteins. Since eosinophil activity in patients with CF is strongly correlated with pulmonary function, the assessment of eosinophil granule proteins might be useful for clinical monitoring in CF.