However, plant-derived cysteine protease, papain induces asthma in mice initiated by activation of protease-activated receptor (PAR) signaling pathway and the subsequent production of IL-33, IL-25 and thymic stromal lymphopoietin (TSLP) from airway epithelial cells, followed by secretion of IL-5 and IL-13 by lung group 2 innate lymphoid cells (ILC2s)3,6. Here, TSLP is linked to asthma.