Objective: We investigated whether eosinophil degranulation is a distinctive feature of asthma and can distinguish between chronic cough patients with asthma and those without.
Methods: Thirty-seven patients, with a chronic cough for more than 1 month, and nine normal individuals (controls) were enrolled. Subjects were divided into two groups: one group with asthma and positive bronchial hyperresponsiveness (BHR) (Asthma group, n = 18) and the other group without asthma and negative BHR (Non-Asthma group, n = 19). From induced sputum, total cell counts and differentials were determined. Myeloperoxidase levels were measured by Enzyme-Linked Immunosorbent Assay (ELISA), and eosinophil-derived neurotoxin (EDN) and major basic protein (MBP) levels were measured by radioimmunoassay.
Results: The percentage of sputum eosinophils was increased in the Asthma (p < .001) and Non-Asthma (p < .05) groups compared with the Control group and when comparing the Asthma and Non-Asthma (p < .001) groups. Sputum EDN and MBP levels were increased in the Asthma group compared with the Non-Asthma (p < .05 and p < .05, respectively) and Control groups (p < .05 and p = .055, respectively). However, EDN and MBP levels were not increased in the Non-Asthma group compared with the Control group. The percentage of sputum eosinophils in the Asthma group correlated positively with sputum EDN (Rs = 0.921, p < .001) and MBP (Rs = 0.882, p < .0001) levels and negatively with maxΔFEV(1) (Rs = -0.501, p < .05) (FEV(1), forced expiratory volume in 1 second). Unexpectedly, the percentage of eosinophils in the Non-Asthma group did not correlate significantly with any of these markers. Increased EDN and MBP levels and significant correlations between the percentage of eosinophils and EDN and MBP were only observed in asthma patients.
Conclusions: These findings suggest that eosinophil degranulation is more important than eosinophilia in identifying asthma.