In order to find the substrate of E3 ubiquitin ligase PELI1 and TRAF3's possible E3 ubiquitin ligase, we pulled down the lysate of mouse hepatocellular carcinoma infiltrating Th17 cells with anti-PELI1 or -TRAF3 antibodies, and isolated the protein-antiboy-magnetic bead complex by electrophoresis. Mass spectrometry was performed to look for proteins that might bind PELI1 or TRAF3.