Expression of the apoptosis inhibitor Bcl‐2 in sputum eosinophils from children with acute asthma

Abstract

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. 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. 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). 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.