Eosinophils in the Spotlight: Eosinophilic airway inflammation in nonallergic asthma

in vivo?The recent DREAM study reported that subcutaneous injection with IL-5-specific antibody reduced asthma exacerbations in subjects with severe asthma.As the study did not stratify patients according to BMI and only measured reduction of eosinophil numbers in sputum 10 , associations between drug efficacy and BMI were not reported; however, this may be an important association to consider in future trials.In the developed world, where parasitic infections are relatively uncommon, circulating eosinophils are rare, but the incidences of the metabolic syndrome and asthma are increasing.In contrast, in developing countries, where people commonly have intestinal parasites and concomitantly high levels of circulating eosino-phils and plasma IL-5, metabolic syndrome and obesity are rare, as is the incidence of asthma.Perhaps this may be partly explained by the function of eosinophils being directly related to their distribution within visceral tissues-either adipose tissue or the airway wall, as shown in mice (Fig. 1).The fact that lung tissue eosinophil numbers directly correlate with BMI indicates that the interaction with local stromal cells might determine their function.It would be very interesting to further understand whether the visceral fat of patients with asthma harbors eosinophils in numbers comparable to that of individuals without asthma, independent of their BMI.It is also conceivable that there may be a distinct population of tissue eosinophils that reside within the visceral fat and perform a homeostatic role, whereas bone marrow-derived eosinophils are important during inflammation.Given that the incidence of both asthma and obesity is increasing at an alarming rate, a greater understanding of the role of eosinophils in glucose homeostasis and in patients with asthma is now warranted to provide more accurate phenotype-driven therapy.