Tumor necrosis factor receptor superfamily member 9(TNFRSF9) is a member of the tumor necrosis factor (TNF) receptor family. It can be induced by lymphocyte activation (ILA) and is expressed by activated T cells, but to a larger extent on CD8 than on CD4 T cells. In addition, TNFRSF9 expression is found on dendritic cells, follicular dendritic cells, natural killer cells, granulocytes and cells of blood vessel walls at sites of inflammation. As receptor for TNFSF9/4-1BBL, it can activate T cells and the cross-linking of this protein can enhance T cell proliferation, IL-2 secretion survival and cytolytic activity. Further, it can enhance immune activity to eliminate tumors in mice.