CD157 is an ectoenzyme member of the ADP-ribosyl cyclase family, also known as ADP-ribosyl cyclase 2, BST-1 (bone marrow stromal cell antigen 1), BP-3 antigen. It has a molecular weight between 40 - 46 kD and is a GPI-linked cell membrane glycoprotein which is expressed as a homodimer. CD157 is expressed by macrophages, neutrophils, bone marrow stromal cells, endothelial cells, follicular dendritic cells, and T and B cell progenitors prior to the rearrangement of the antigen receptors. Besides the ectoenzyme activity, it also plays a role in neutrophil migration and adhesion.