M-BYF treatment significantly alleviated type 2 airway inflammation, AHR, mucus hypersecretion and collagen deposition in experimental allergic asthma, which was related to the decrease of expansion/differentiation and activities of ILC2s and Th9 cells, as well as to the inhibition of VIP–VPAC2 signalling. The gene discussed is VIP; the disease is allergic asthma.