Tumor necrosis factor (TNF), lymphotoxin-α (LTα) and LTD are related cytokines which belong to the TNF ligand family and are encoded by genes clustered within the MHC gene complex [1, 2]. TNF and LTa self-associate as homotrimers, capable of binding both the 55-60 KD TNF receptor 1 (TNFRp55) and the 75-80 KD TNF receptor 2 (TNFRp75) [3]. In addition, LTα also binds herpes simplex virus (HSV) entry mediator (HVEM) which is an orphan member of the TNF receptor family [4-6]. LTD exists in a heterotrimeric complex with LTa, which solely binds the lymphotoxin-D receptor (LTβR)[1, 7–10]. Recently, a novel ligand which shares homology with TNF family members has been found and termed LIGHT [4]. Like the other ligands, LIGHT forms a homotrimer and is capable of binding two receptors, HVEM and LTβR [4] (see Fig. 1).