– Tumor necrosis factor ligand superfamily member 4(TNFSF4/OX40L) is a single-pass type II membrane protein. OX40L is expressed by DCs, macrophages and B cells and signals via its cognate receptor OX40 which is mainly expressed on APCs. OX40L/OX40 interactions are important in T-cell activation and survival and for the generation of memory T cells from activated effector T cells. It is a cytokine that binds to TNFRSF4, Co-stimulates T-cell proliferation and cytokine production. OX40L/OX40 interactions are important in T-cell activation and survival and for the generation of memory T cells from activated effector T cells.