Does eosinophil cationic protein in sputum and blood reflect bronchial inflammation and obstruction in allergic asthmatics?

In the assessment of asthma severity and monitoring of asthma drug therapy, eosinophils and eosinophil cationic protein (ECP) have been identified in blood but rarely in sputum. The aim of our study was to determine if ECP concentrations in blood and sputum reflect bronchial inflammation and obstruction in allergic asthmatics and if inhaled steroids influence this relationship. We carried out a descriptive, cross-sectional study of 42 allergic asthmatic outpatients from a respiratory medicine department, of whom 22 were on beta 2-adrenergic agonists only and 20 were treated with low doses of inhaled steroids. Spirometry and methacholine challenge were performed and eosinophils and ECP values in induced sputum and blood were determined. The age and FEV1 were similar in both groups. It was found that in patients receiving inhaled steroids, the methacholine PD20 was higher than in patients on beta 2-adrenergic agonists only. However, there were no significant differences in serum and sputum ECP between the groups (median 14.5 micrograms/l vs. 17.2 micrograms/l and 235 micrograms/l vs. 301 micrograms/l, respectively). In patients not receiving steroids, sputum ECP correlated positively with eosinophils in sputum (r = 0.61, p < 0.01) and inversely with FEV1 (r = -0.43, p < 0.05). Serum ECP correlated with blood eosinophils and methacholine PD20. In patients treated with inhaled steroids most correlations were no longer significant. We concluded that ECP in sputum, rather than in blood, seems to reflect both eosinophilic inflammation and bronchial obstruction in asthmatics not receiving inhaled steroids. Asthmatics on low doses of inhaled steroids had increased ECP levels in sputum and serum, indicating persistent eosinophilic inflammation of the airways.