CD73 is a glycosyl-phosphatidylinositol (GPI)-anchored adhesion protein that catalyzes the dephosphorylation of extracellular purine and pyrimidine nucleotides to their corresponding bioactive nucleosides. CD73 is a dimer of two identical subunits that depends on GPI to link with the external face of the plasma membrane. Similar to other GPI-anchored proteins，CD73 mediates co-stimulatory signals in T cell activation. CD73 has few structural variants，yet elicits diverse biological function through differential regulation in endothelial cells (EC)，subpopulations of B and T cells，germinal center follicular dendritic cells and on thymic medullary reticular fibroblasts. For example，IgG mediated neutralization of CD73 interferes with lymphocyte adhesion to EC，and blocks aggregation of germinal center B cells and follicular dendritic cells. Furthermore，IgG-mediated targeting of lymphocyte CD73，but not of endothelial cell CD73，causes shedding of CD73 and tyrosine phosphorylation of proteins.