CD38 (T10) is a single chain 42 to 46 kDa type II integral transmembrane glycoprotein with a short N terminal cytoplasmic tail. CD38 is highly expressed on thymocytes. It is also expressed by early cells of B and T lineages, NK cells, plasma cells, monocytes and macrophages and may be detected on cells from multiple myeloma, ALL (B and T) and some AML. It is expressed by murine, but not human, hematopoietic progenitors. In normal lymph nodes and tonsils the antigen is detected mainly on B cells in germinal centers and in plasma cells. The extracellular domain of the molecule shares a high homology sequence with Aplysia ADP ribosyl cyclase. CD38 functions as a multicatalytic ectoenzyme serving as ADP ribosyl cyclase, ADPR hydrolase and possibly NAD+ glycohydrolase, or as a surface receptor.

In mice, CD38 is expressed by follicular B cells, is down regulated on germinal centre B cells, and is not expressed by mature plasma cells. Murine CD38 is also expressed by all Mac1+ macrophages in the peritoneal cavities of unimmunized mice, but not by unstimulated bone marrow derived macrophages. This pattern of expression contrasts strikingly with that seen in the human. 

Monoclonal antibodies to CD38 have been shown to be useful in subtyping of lymphomas and leukemias, inhibition of B lymphopoiesis, detection of plasma cells, protection of B cells from apoptosis, and as a marker for activated B and T cell proliferation.