Serum eosinophil cationic protein as a marker of eosinophilic inflammation in asthma

Background The serum level of eosinophil cationic protein (ECP) has been used as a clinical marker in asthma, on the assumption that it reflects ongoing eosinophilic inflammation of the airways. However, only a few studies have investigated this issue, using bronchial secretions but not tissue specimens. Objective To evaluate cross-sectionally the correlation between serum ECP level or blood eosinophil count, and the degree of eosinophilia in bronchoalveolar lavage fluid (BALF) and bronchial biopsy tissue, and disease activity, in asthmatic patients. Methods Thirty-three adults with symptomatic asthma and six healthy controls were studied. The blood eosinophil count, ECP levels in serum and BALF, percentage of eosinophils in BALF, number of eosinophils in bronchial tissue, pulmonary function, and methacholine bronchial responsiveness of these subjects were clarified. An asthma severity score and inhaled β2-agonist requirement (puffs/day) were also assessed for the asthmatic patients. Results The asthmatic patients, compared with the controls, had more obstructive (as tested by %FEV1, FEV1/FVC, and FEF25–75%) and more responsive airways, and showed a significant increase in the number of eosinophils in the blood, BALF, and tissue, and in the serum ECP levels. The ECP levels in BALF were below the detection limit for most of the subjects in both groups examined. In the asthmatic patients, serum ECP level demonstrated correlations with the number or percentage of eosinophils in BALF and tissue, whereas the blood eosinophil count correlated only with the percentage of eosinophils in BALF. Serum ECP level correlated with all indices of disease activity examined; %FEV1, FEV1/FVC, FEF25–75% bronchial responsiveness, severity score and β2-agonist usage, whereas the blood eosinophil count correlated only with %FEV1 and bronchial responsiveness. Conclusion The data suggest that serum ECP level reflects the intensity of eosinophilic airway inflammation, as well as the disease activity, and may be useful as an inflammatory marker in asthma.