CD38(cluster of differentiation38), also known ascyclic ADP ribose hydrolaseis aglycoproteinfound on the surface of many immune cells (white blood cells), includingCD4+,CD8+,B lymphocytesandnatural killer cells. CD38 also functions incell adhesion,signal transductionandcalcium signaling. In humans, the CD38 protein is encoded by the CD38 gene which located on chromosome 4.