Herpes Virus Entry Mediator (HVEM, TR2) is a type I transmembrane protein of TNF-receptor superfamily. This receptor was identified as a cellular mediator of herpes simplex virus (HAS) entry. Binding of HSV viral envelope glycoprotein D to this receptor has been shown to be part of the viral entry mechanism. It is expressed on most cell types, including T cells, B cells, monocytes, neutrophils, and dendritic cells. It is also found in brain, heart, kidney, liver, and other organs. The ligands of HVEM are LIGHT, BTLA, LTalpha, and CD160. HVEM activates NF-kB through the TNF-related cytokine LIGHT to serve as a costimulatory pathway during T cell activation. HVEM also functions as a ligand for the Ig superfamily members B and T lymphocyte attenuator (BTLA) and CD160 to deliver a coinhibitory signal and limit inflammatory responses initiated by T cells. HVEM plays an important role in regulating lymphocyte activation and homeostasis in immune responses.