In PSC and associated IBD, the potential mechanism of actions includes [3] (1) selective effect on Gram-positive species due to its relatively narrow antibiotic spectrum; (2) reduction of the hydrophobic secondary bile acids, which are potentially responsible for the right-sided colitis and after absorption through the enterohepatic circulation for mediating the bile duct injury; and (3) immunomodulatory effect of vancomycin via the tumor necrosis factor (TNF)–alpha inflammatory pathways and/or downstream Treg induction. The gene discussed is TNF; the disease is colitis.