The AD2 antibody reacts with human CD73, a glycosyl phosphatidylinositol (GPI)-anchored glycoprotein and ecto-5’-nucleotidase expressed on the surface of subsets of B and T cells, follicular dendritic cells, mesenchymal stem cells, endothelial cells, and epithelial cells. CD73 catalyzes the hydrolysis of 5’-adenosine monophosphate (AMP) to form the bioactive nucleoside adenosine, and plays a pivotal role in the activation of P1 adenosine receptors by regulating extracellular adenosine concentrations. CD73 also appears to function as a co-signaling molecule on T cells and as an adhesion molecule mediating lymphocyte interactions with the endothelium and follicular dendritic cells. CD73 is used as a marker for lymphocyte differentiation, its expression increasing during development. It is also a useful marker for identifying undifferentiated mesenchymal stem cells. CD73 is highly expressed in many types of human and mouse cancers, and has been implicated in the control of tumor growth.