Human CD38 is a 45 kDa type II trans-membrane glycoprotein with a peculiar
discontinuous pattern of expression in leukocytes, although evidence is acc
umulating of its quite widespread expression outside of the hematopoietic s
ystem. CD38 is a member of an emerging family of cytosolic and membrane-bou
nd enzymes whose substrate is nicotinamide adenine dinucleotide (NAD), a co
enzyme ubiquitously distributed in nature. CD38 is a multifunctional molecu
le able to exert not only an enzymatic activity but also to mobilize calciu
m, to transduce signals, to adhere to hyaluronan and to other ligands. Inte
raction with CD38 on various leukocyte subpopulation has profound though di
verse effects on their life-span, however, the immunoregulatory activities
seem to be independent of the enzymatic functions of the molecule.