LIGHT is a relatively new member of the TNF family of membrane-anchored ligands that signals via two receptors: herpesvirus entry mediator (HVEM) and lymphotoxin (LT) в receptor (LT/bR). LIGHT also interacts with the decoy receptor type 3 (DcR3) (Yu et al, 1999). LIGHT is closely related to LTa and \SX3 as defined by amino acid sequence homologies and shared receptor specificity. LIGHT exhibits inducible but transient expression on the surface of activated T lymphocytes. The receptor-binding specificity for the LT/bR suggests that LIGHT will be involved in lymphoid tissue organization. The high level of expression of HVEM on lymphoid cells further suggests that LIGHT may regulate T cell and В cell differentiation. LIGHT also acts as an interference factor that can block herpes simplex virus 1 (HSV) entry into cells, and may thus act as a host deterrent to virus infection.