Recent work has highlighted the role of innate cell populations in triggering this response: following infection, production of ‘alarmin’ cytokines (IL-25, IL-33 and TSLP) by epithelial cells stimulates innate lymphoid cells (ILCs, also termed nuocytes) to produce type 2 cytokines, in particular IL-5 and IL-13 [12••,13••,14••]. Here, TSLP is linked to infection.