The relationship of eosinophil granule proteins to ions in the sputum of patients with cystic fibrosis

Background Increased sputum levels of eosinophil granule proteins have been reported despite normal eosinophil numbers in peripheral blood and in the lung in cystic fibrosis (CF). Mechanisms of eosinophil priming and activati on are still unclear in CF. Objective In the present study we investigated whether ion concentrations i n the sputa of CF patients are related to eosinophil activity. Methods We assessed concentrations of eosinophil cationic protein (ECP), eo sinophil protein X (EPX), major basic protein (MBP) and ions (Na+, Cl-, Ca2 +, Mg2+) in sputum samples of 29 children with CF as well as in 10 controls with bronchial asthma. Results Patients with CF demonstrated significantly higher levels of ECP, N a+, Cl- and Ca2+ levels than asthmatics (P < 0.04, P < 0.0001, P < 0.0001, P < 0.02). No differences were seen between concentrations of EPX and Mg2in the two groups. In CF, eosinophil granule proteins correlated significan tly with Ca2+ and Mg2+ concentrations (ECP, P < 0.0001, r = 0.65, P < 0.000 1, r = 0.66; MBP, P < 0.03, r = 0.41, P < 0.03, r = 0.42), furthermore inve rsely with Cl- concentrations (ECP, P < 0.0003, r = - 0.63; EPX, P < 0.02, r = - 0.45; MBP, P < 0.03, r = - 0.41) but not with Na+ levels. ECP, Na+ an d Cl- were also correlated with lung function variables (FVC, P < 0.04, - 0 .38, P < 0.02, r = 0.44, P < 0.03, r = 0.41; FEV1, P < 0.007, 1- = - 0.49, P < 0.006, r = 0.5, P < 0.008, r = 0.48; MEF50, P < 0.003, r = - 0.54, NS, P < 0.03, r = 0.42; MEF25, P < 0.039, r = - 0.4, P < 0.005, r = 0.51, P < 0 .05, r = 0.37). Conclusion Our results demonstrated a significant relationship of eosinophi l degranulation and ions in CF, indicating that ion composition in CF sputa may be at least partly be responsible for high levels of eosinophil produc ts despite low eosinophil numbers.