Human CD154 (CD40 Ligand) Recombinant Protein. CD40 Ligand (CD40-L), or CD154, is a membrane glycoprotein and differentiation antigen expressed on the surface of T cells. The CD40 Ligand stimulates B cell proliferation and secretion of all immunoglobulin isotypes in the presence of cytokines. CD40 Ligand 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 IL-2.