CD40 Ligand (CD40L), a member of the TNF superfamily of ligands, is expressed as either a membrane-bound or soluble homotrimer (1). Both membrane-bound and soluble forms of CD40L have biological activity (1,2). CD40L is expressed primarily on activated T cells; however, mast cells, basophils, and NK cells may also express CD40L (1). CD40L functions as an important T cell co-stimulatory molecule and enhances T-dependent B cell responses (1,2). CD40L binds CD40, which is a receptor expressed on B cells, dendritic cells, and macrophages (1). Binding of CD40L to CD40 leads to the recruitment of TRAF proteins (TRAFs 2,3,5, and 6) resulting in the activation of the JNK and NF-κB pathways (1,2).
