Human TWEAK is a new secreted ligand in the tumor necrosis factor family that weakly induces apoptosis. TWEAK, like many other members of the TNF family, is able to induce interleukin-8 synthesis in a number of cell lines. The recombinant human TWEAK is a 17.0 kDa protein, comprising the TNF-like extraCellular domain of TWEAK.