Major basic protein, but not eosinophil cationic protein or eosinophil protein X, is related to atopy in cystic fibrosis

Increased eosinophil granule proteins have been described in serum and sputum samples of patients with cystic fibrosis (CF). It has been assumed that eosinophil degranulation is enhanced in atopic subjects - as in asthmatics. Since in CF no differences in eosinophil cationic protein (ECP), eosinophil protein X (EPX), and eosinophil peroxidase between atopic and nonatopic subjects have been detected, we investigated whether major basic protein (MBP) is increased in serum and sputum samples derived from atopic (n=14) compared with nonatopic CF subjects (n=26). In CF patients, high mean serum (sputum) levels of ECP 29.7 μg/I (2.7 mg/I), EPX 53.7 μg/I (7.9 mg/I), and MBP 984.6 μg/I but low sputum MBP levels (57.4 μg/I) were measured. In addition, in serum and in sputum samples, a significant correlation between MBP and ECP (P<0.03 and P<0.0001, respectively) or EPX (P<0.05 and P<0.0004, respectively) was detected. By subdivision of the patients into allergic and nonallergic subjects, significant differences were found for serum MBP values only (mean 1382.2 μg/I vs 770.5 μg/I; P<0.0001), but not for ECP or EPX serum levels or for eosinophil proteins in sputum. Although no differences between atopic and nonatopic CF patients in ECP and EPX were found, serum MBP levels were higher in patients sensitized to inhalant allergens than in nonsensitized subjects. These results indicate differential release of eosinophil granule proteins in peripheral blood from eosinophils, and they also indicate that MBP in serum likely is to be a better discriminator of atopy in CF.