The cluster of differentiation (CD) system is a glycosyl phosphatidylinositol anchored membrane protein thatbelongs to the CD38 family.It is generally used in immunophynotyping. CD157 was discovered in a bonemarrow stromal cell line where it facilitates pre-B-cell growth. CD157 is a bifunctional ectoenzyme that exhibitsboth ADP-ribosyl cyclase and cyclic ADP ribose hydrolase activities followed with CD38. It plays a role inrheumatoid arthritis (RA) due to its enhanced expression in RA-derived bone marrow stromal cell lines. Studieshave shown that this protein have a role in predicted to function as a cell surface receptor and animmunoregulatory molecule.