Although the mechanisms of larval killing are less well-studied, it is known that early in infection, prior to adult worm development and establishment, mucosal epithelial sensor cells secrete a group of alarmins—for example, IL-25, thymic stromal lymphopoietin (TSLP), and IL-33—that promote the activation and differentiation of innate and adaptive type 2 cells, leading to the secretion of a myriad of cytokines, including IL-4, IL-5, IL-9, and IL-1326,27. The gene discussed is IL9; the disease is infection.