Although Th2 cells are at the heart of asthma pathogenesis, group 2 innate lymphoid cells (ILC2s) have gained interest in recent years because of their ability to produce type 2 cytokines and because they can be activated by the epithelial-derived alarmins IL-33, IL-25, and TSLP (Fig. 1, left). Here, IL33 is linked to asthma.