Total protein of psoriasis skin samples was collected and dilution to 1 ml. 1 μg Recombinant Human GPCR MRGX2 protein (GST tag, Abcam, Cambridge, UK) was added into the protein solution, rotate for 4 h at room temperature. Then the anti-GST magnetic bead (BD, New Jersey, USA) was used for get the binding protein of MRGPRX2. Polypeptide segments were detected by liquid chromatography-mass spectrometry. Moreover, the Targeted Proteomics was used to prove BD1, BD3, LL-37, S00A9 and S100A6 (n=3).