MRGPRX2 and allergic asthma: Therefore, it is likely that hemokinin-1 (HK-1) produced from lung macrophages, bronchial cells and mast cells [59,60], as well as ligands generated from eosinophils [61,62], neutrophils [63], and epithelial cells [64], further activate mast cells via MRGPRX2 to release inflammatory mediators and thereby amplify airway hyper-responsiveness, resulting in allergic asthma exacerbation [65].