Background Obese asthmatics are known to have reduced eosinophils in sputum, as well as poor control of asthma symptoms.¹ We have shown that, compared to non-obese patients, there is an elevated number of eosinophils in the airway submucosa of obese asthmatic patients.² This study aims to determine whether a differential susceptibility to apoptosis, between obese and non-obese patients, could contribute to these clinical observations.

Method Patients with a clinical diagnosis of asthma were recruited (n = 28) and consented at Glenfield Hospital for blood donation to study eosinophil apoptosis; the patients recruited had varying severities of asthma and BMI. Eosinophils were isolated from whole blood by negative immunomagnetic selection using CD16 microbeads to a purity of mean ± SD 95.7% (± 4). Purified eosinophils (Time 0) were placed into culture in RPMI (1640 + GlutaMAX-1 supplemented with 10% FBS and 1% penicillin and streptomycin) and harvested at 17 and 21 hours later to measure apoptosis by flow cytometry using Annexin V and Propidium Iodide (Becton Dickinson). Cells were considered apoptotic if they were Annexin V positive/PI negative and reported as a percentage of total eosinophils.

Results At 0 hours, the mean% of annexin V positive cells was 0.47% and there was no significant association with BMI (r = −0247, p value = 0.245). At 17 and 21 hours there were 12.68% and 21.0% annexin V positive cells, respectively, and we noted a significant negative Pearson’s correlation between eosinophil apoptosis and BMI at time 17 (r = −0.449; p = 0.028) and time 21 (r = −0.448; p = 0.028). These correlations were independent of lung function, steroid medication and percentage eosinophil purity.

Conclusion Eosinophils from obese asthmatic patients are less susceptible to apoptosis compared to those from non-obese patients. This may contribute to the differential presence of eosinophils in the lamina propria and airway of obese patients compared to non-obese individuals.

References

1. Haldar P, Pavord ID, Shaw DE, et al. Cluster analysis and clinical asthma phenotypes. Am J Respir Crit Care Med 2008;178(3):218–224.

2. Desai D, Newby C, Symon FA, et al. Elevated sputum interleukin-5 and submucosal eosinophilia in obese individuals with severe asthma. Am J Respir Crit Care Med 2013;188(6):657–663.