A mysterious cytokine quells asthma by triggering regulatory T (T reg) cells that prevent dendritic cells from growing up, Semitekolou et al. reveal (page 1769).
Like many cytokines, activin-A triggers different effects in different situations. In some studies, it incited inflammation, but in others it had the opposite effect. The abundance of activin-A in the blood of patients with asthma and in the lungs of mice with inflamed airways suggests a role for the protein in allergy and asthma. But whether the cytokine exerts pro- or anti-inflammatory effects during these reactions remains unclear.
Semitekolou et al. addressed the issue by dosing asthmatic mice with an activin-blocking antibody shortly before the animals inhaled an allergen. Asthma symptoms were more severe in treated rodents than in controls. And injections of activin-A helped mice breathe easier.
Activin-A exerted its effects in part by boosting the number of T reg cells. In vitro, these T reg cells squelched Th2 responses and when transferred into mice, they alleviated asthma symptoms. The T reg cells worked by releasing the soothing cytokines interleukin-10 and TGF-β1 and by blocking maturation of dendritic cells, which are essential for Th2 specialization. ML
