Taylor and colleagues1 demonstrated a significant association between asthma severity and obesity. However, the mechanisms underlying this association are not fully understood. We suggest that the increase in asthma severity in obese patients might also be related to a defective function of regulatory T cells (Tregs).

Tregs play an essential role in immune homeostasis and protection against autoimmunity, and it has been suggested that the function of Tregs may be defective in patients with asthma.2 On the other hand, leptin, a known hormone marker for obesity, exerts actions on multiple organ systems, including the immune system. Indeed, it has been shown that leptin signalling negatively modulates Treg function.3

Therefore, the increase in asthma severity observed in obese patients might by caused, in part, by a decreased immunological tolerance induced by a decreased function of Tregs mediated by leptin. Moreover, it has been suggested that induction of Treg development might be a useful tool for asthma treatment.2 However, Treg increases might also increase cancer risk by impairing host antitumor immune response.4 Thus the safest way to improve asthma in obese patients is to lose weight.