CD40L [CD154] (human):Fc (human) (rec.)

CD40 Ligand (CD40L), renamed TNFSF5 but now also known as CD154, TRAP and gp39, is a 34-39kDa type II transmembrane glycoprotein that belongs to the TNF superfamily. As with other TNF superfamily members, CD40L will exist as a trimer, both as a membrane bound and soluble form. Multiple mutations and alternate splice forms of CD40L exist, often associated with pathology and leading to truncated or nontrimerizable forms of CD40L. CD40L binds to both CD40 and to integrin αIIbβ3 (CD41). In the cell membrane, it also associates with a unique splice variant of CD28 (CD28i) that may facilitate CD40L signal transduction. CD40L is expressed by monocytes, NK cells, mast cells, basophils, smooth muscle cells, endothelial cells, dendritic cells,activated and resting B cells, plus activated platelets and CD4⁺ T cells. CD40L ligation of CD40 on dendritic cells (DC) initiates DC maturation and differentiation. CD40L signaling into naive B cells promotes germinal center formation and isotope switching. CD40-CD40L seems to bridge innate and adaptive immune signals.