This MAb reacts with a 45kDa glycopeptide, which is a type II membrane glycoprotein with a transmembrane sequence near the NH2terminus. CD38 is a type II transmembrane glycoprotein that is present on early B- and T-cell lineages and activated B- and T-cells but is absent from most mature resting peripheral lymphocytes. CD38 is also found on thymocytes, pre-B cells, germinal center B-cells, mitogen-activated T-cells, monocytes and Ig-secreting plasma cells. CD38 is expressed on CD34+ cells. The CD34+CD38- population of hematopoietic stems cells defines the most pluripotent cells (e.g. blast colony forming cells).