P241 Eosinophil apoptosis is negatively associated with body mass index in asthma

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 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. 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.