Characterization of a new member of the TNF family expressed on antigen presenting cells

The TNF family is involved in the regulation of the immune system, and its members have been implicated in a variety of biological events such as apop tosis, cell proliferation, differentiation and survival. Here we present a new member of the TNF family, tumor necrosis factor super family member 20 (TNFSF20) that we have identified from the expressed sequence tag (EST) dat abase and characterized. The human protein is a 285 amino acid long type II transmembrane protein and is 19% homologous to TNF in its extra-cellular d omain. TNFSF20 is expressed at the surface of antigen presenting cells such as cells of the macrophage-monocyte lineage and dendritic cells. After tre atment with bacterial lipopolysaccharide (LPS), TNFSF20 expression is downr egulated at the surface of the expressing cells, suggesting that the membra ne-bound protein gets cleaved, and that a soluble factor is released in the extra-cellular compartment. The soluble form of the recombinant TNFSF20 in duces proliferation of resting peripheral blood monocytes (PBMC) and cell d eath of activated lymphocytes. TNFSF20 might therefore play a critical role in the regulation of cell-mediated immune responses.