Obesity-Associated Asthma in Children A Distinct Entity

Background: Obesity-associated asthma has been proposed to be a distinct entity, differing in immune pathogenesis from atopic asthma. Both obesity-mediated inflammation and increase in adiposity are potential mechanistic factors that are poorly defined among children. We hypothesized that pediatric obesity-associated asthma would be characterized by T helper (Th) 1, rather than the Th2 polarization associated with atopic asthma. Moreover, we speculated that Th1 bio-markers and anthropometric measures would correlate with pulmonary, function tests (PFTs) in obese asthmatic children. Methods: We recruited 120 children, with 30 in each of the four study groups: obese asthmatic children, nonobese asthmatic children, obese nonasthmatic children, and nonobese nonasthmatic children. All children underwent pulmonary function testing. Blood was collected for measurement of serum cytokines. T-cell responses to mitogen, phorbol 12-myristate 13-acetate (PMA), or antigens tetanus toxoid or Dermatophagoides farinae were obtained by flow cytometric analysis of intracellular cytokine staining for interferon-gamma (IFN-gamma) (Th1) or IL-4 (Th2) within the CD4 population. Results: Obese asthmatic children had significantly higher Th1 responses to PMA (P < .01) and tetanus toxoid (P < .05) and lower Th2 responses to PMA (P < .05) and D Prime (P < .01) compared with nonobese asthmatic children. Th-cell patterns did not differ between obese asthmatic children and obese nonasthmatic children. Obese asthmatic children had lower FEV1/FVC (P < .01) and residual volume/total lung capacity ratios (P < .005) compared with the other study groups, which negatively correlated with serum interferon-inducible protein 10 and IFN-gamma levels, respectively. PM's, however, did not correlate with BMI z score or waist to hip ratio. Conclusions: We found that pediatric obesity-associated asthma differed from atopic asthma and was characterized by Th1 polarization. The altered immune environment inversely correlated with PFTs in obese asthmatic children. CHEST 2012; 141(4):895-905