CD40 is a cell surface receptor that is expressed on the surface of all mature B cells and also expressed on monocytes, dendritic cells, and thymic epithelium. CD40 is a member of the tumor necrosis factor(TNF) receptor superfamily and is the receptor for CD40 ligand. CD40 ligand(CD40L, CD154, gp39, and TRAM) belongs to the TNF gene family and is expressed more widely than CD40 predominantly on activated CD4+ T cells. Activation of CD40 has also been shown to inhibit the growth of certain B cell lymphomas and to induce the death of transformed cells of mesenchymal or epithelial origin.
