Its classification as biased is based on studies in cell lines such as the HEK293-derived TANGO Luciferase Assay cell line (HTLA) and the Laboratory of Allergic Diseases 2 mast cell line (LAD2), naturally expressing MRGPRX2 [20,21,22], or MRGPRX2 transfectants [20,23,24,25,26]. Here, MRGPRX2 is linked to allergic disease.