Subramanian H, Gupta K, Ali H. Roles of Mas-related G protein-coupled receptor X2 on mast cell-mediated host defense, pseudoallergic drug reactions, and chronic inflammatory diseases. J Allergy Clin Immunol. 2016;138(3):700-710. doi:10.1016/j.jaci.2016.04.051 For example, while ciprofloxacin and levofloxacin activate MrgprB2 (mice) with EC50 values of ~126 μg/ml and 807 μg/ml, respectively, the same drugs activate MRGPRX2 (human) with EC50 values of ~6.8 μg/ml and 23 μg/ml. Porebski Grzegorz, Kwiecien Kamila, Pawica Magdalena, Kwitniewski Mateusz. Mas-Related G Protein-Coupled Receptor-X2 (MRGPRX2) in Drug Hypersensitivity Reactions. Frontiers in Immunology 2018;9:3027. DOI:10.3389/fimmu.2018.03027 Downstream signaling from MRGPRX2 involves activation of the phospholipase C-beta pathway, which ends in the release of the preformed and the de novo synthesized mediators (26, 48). MRGPRX2-mediated responses seem to be more rapid, but transient in comparison to IgE-triggered events (33, 48). Jue Wang, Yongjing Zhang, Chaomei Li, Yuanyuan Ding, Shiling Hu, Hongli An. Inhibitory function of Shikonin on MRGPRX2-mediated pseudo-allergic reactions induced by the secretagogue. Phytomedicine 2020; 68: 153149. Doi:10.1016/j.phymed.2019.153149.