CD38 is a glycoprotein that is present on the surface of various immune cells, including CD4+, CD8+, B cells, and natural killer cells. It serves as a marker of cell activation. The CD38 protein has been associated with several conditions and processes such as HIV infection, leukemias, myelomas, solid tumors, type II diabetes mellitus, bone metabolism, and certain genetically determined conditions. It has also been used as a prognostic marker in leukemia.

CD38 is highly expressed on thymocytes and is also found on early cells of B and T lineages, natural killer cells, plasma cells, monocytes, and macrophages. It can be detected on cells from multiple myeloma, acute lymphoblastic leukemia (B and T cell), and some forms of acute myeloid leukemia.

The CD38 antibody has various applications, including the 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.