– CD38, also called ADP-ribosyl cyclase, is a Type II integral membrane protein with 301 amino acids in length that belongs to the ADP-ribosyl cyclase family.It synthesizes the second messagers cyclic ADP-ribose and nicotinate-adenine dinucleotide phosphate, the former a second messenger for glucose-induced insulin secretion. And also moonlights as a receptor in cells of the immune system. CD38 is expressed in B and T lymphocytes, osteoclasts, and in cardiac, pancreatic, liver and kidney cells. Through its production of cyclic ADP-ribose, CD38 modulates calcium-mediated signal transduction in many types of cells, including neutrophils and pancreatic beta cells.