CD40 Ligand (CD40LG) is a type II transmembrane glycoprotein that belongs to the TNF superfamily. Like other TNF superfamily members, CD40LG exists as a trimer in membrane bound and soluble form, both of which are bioactive. CD40LG is a ligand for CD40; its ligation also initiates signal transduction in CD40LG expressing cells. CD40LG is a differentiation antigen that is expressed on the surface of T-cells. It stimulates B-cell proliferation and secretion of all immunoglobulin isotypes in the presence of cytokines. CD40LG has been shown to induce cytokine production and tumoricidal activity in peripheral blood monocytes. It also co-stimulates proliferation of activated T-cells and this is accompanied by the production of IFN-gamma, TNF-alpha, and IL2.