The CD38 molecule is a glycoprotein that spans the cell membrane, weighing approximately 46-kDa, featuring a brief sequence of 20 amino acids at its N-terminal end within the cytoplasm, and a substantial 256 amino acid section extending outside the cell. It can be found on a wide array of blood-related cells, most notably plasma cells, as well as within particular solid tumor tissues. CD38 serves as an indicator that appears early during the activation process of B-cells that have not yet encountered an antigen, proving valuable for pinpointing specific functional groups of fully developed B-lymphocytes.