MCA4637T recognises human CD258, otherwise known as LIGHT (ligand for herpesvirus entry mediator), a 30kDa type 2 transmembrane member of the tumour necrosis factor ligand superfamily. It is a ligand for tumour necrosis factor receptor-like 2 (also known as herpesvirus entry mediator or HVEM). It also activates NFKB, stimulates the proliferation of T-cells and acts as a receptor for Herpes simplex virus. LIGTH inhibits the growth of some tumour cells and plays a role in intestinal inflammation. It is predominantly expressed in the spleen, but is also found in the brain and is weakly expressed in the heart, lung, liver, appendix and kidney.