Human CD38, a surface receptor, an enzyme, an adhesion molecule and not a simple marker.

Human CD38 is a 45 kDa type II trans-membrane glycoprotein with a peculiar discontinuous pattern of expression in leukocytes, although evidence is accumulating of its quite widespread expression outside of the hematopoietic system. CD38 is a member of an emerging family of cytosolic and membrane-bound enzymes whose substrate is nicotinamide adenine dinucleotide (NAD), a coenzyme ubiquitously distributed in nature. CD38 is a multifunctional molecule able to exert not only an enzymatic activity but also to mobilize calcium, to transduce signals, to adhere to hyaluronan and to other ligands. Interaction with CD38 on various leukocyte subpopulation has profound though diverse effects on their life-span, however, the immunoregulatory activities seem to be independent of the enzymatic functions of the molecule.