TALL-1(tumor necrosis factor and apoptosis ligand-related leukocyte-expressed ligand 1), a member of the TNF family, is a novel cytokine identified recently. The human and mice TALL-1 consist of 285 and 309 amino acids, respectively. It was shown that TALL-1 is a type Ⅱ transmembrane protein which is produced in monocytes and macrophages. A soluble form of human TALL-1(sTALL-1) has a extracellular domain composed of 152 amino acids which corresponds to C-terminal 134～285 site of amino acids. The recombinant human sTALL-1 is functionally involved in stimulating B cell growth, activating NF-κB(nuclear factor-kappa B) and JNK(c-Jun NH₂-terminal kinase), and inhibiting tumor cell growth. Moreover, the overexpression of TALL-1 in transgenic mice can result in severe B cell hyperplasia and autoimmune lupus-like disease. Therefore, TALL-1 functions as a potent regulatory factor in vivo and in vitro.