CD38 (Cluster of Differentiation 38) is a glycoprotein found on the surface of many leukocytes, including CD4+, CD8+, natural killer cells, thymus cells, lg secreting plasma cells, early cells of B and T lineages and on activated T and B cells. It is not found on most mature resting peripheral lymphocytes. CD38 also functions in cell adhesion, signal transduction and calcium signaling. This antibody is a marker of cell activation that has been connected to HIV infection, leukemias, myelomas, solid tumors, type II diabetes mellitus, and bone metabolism.