Background Apoptosis of eosinophils is of increasingly important value in modulating allergic airway inflammation in asthma. Our purpose was to investigate the degree of expression of the antiapoptotic B-cell lymphoma/leukaemia-2 (Bcl-2) protein in sputum eosinophils during acute asthma exacerbation and its relationship with exacerbation severity.
Methods Sputum was obtained from 33 asthmatic children and 15 healthy children as a control group. Patients were studied during an acute asthma exacerbation. They were classified according to the severity of exacerbation into mild, moderate and severe (n=11 for each). Patients with severe exacerbation were followed up until remission and another sputum sample was obtained. Number of sputum eosinophils was expressed as percentage of leucocytes. Bcl-2 expression in sputum eosinophils was assessed by immunohistochemical staining techniques; the results were expressed as percentage of positively stained cells over total eosinophils.
Results Sputum eosinophils and Bcl-2+ eosinophils' percentages were significantly higher in patients with acute exacerbation than controls (P<0.01). Patients with severe exacerbation had significantly higher sputum Bcl-2+ eosinophils' percentage than those with mild-to-moderate exacerbation (mean±SD=42.4±31.96% vs. 5.7±14.5%, P<0.01). A significant negative correlation was found between Bcl-2+ eosinophils' percentage and peak expiratory flow rate % predicted (P<0.05). After remission, patients with severe exacerbation showed a significant decrease of Bcl-2+ eosinophils' percentage (P<0.05).
Conclusion Our findings suggest that Bcl-2 prolongs survival and decreases apoptosis of airway eosinophils in asthma especially during exacerbation. Eosinophil apoptosis and Bcl-2 represent a target for new and effective therapeutic strategies of asthma.