CD38 (ADP-ribosyl cyclase 1, cyclic ADP ribose hydrolase) is an enzyme that binds CD31 and synthesizes cyclic ADP-ribose and nicotinate-adenine dinucleotide phosphate. It participates in lymphocyte and endothelial cell adhesion, and regulates cell activation and proliferation depending on the environment. In immunohistochemistry, CD38 can be used to identify plasma cells and plasma-blastic differentiation and to help diagnose myeloma. It is a prognostic marker in HIV+ patients, where higher expression of CD38 and CD8 positive T cells correlates with poor prognosis. In B-cell chronic lymphocytic leukemia, increased presence on B-CLL cells is also indicative of poor prognosis. In immunohistochemistry of normal tissues, CD38 has strong positivity on plasma cells, and is found on NK cells, B and T cells, committed hematopoietic progenitor cells monocytes, erythroid and myeloid precursors, basophils, neurons, perivascular autonomic nerve terminals, pancreatic islets, small intestinal lacteals, and thymocytes. References: The UniProt Consortium. Nucleic Acids Res. 47: D506-515 (2019); Nucleic Acids Res. 2016 Jan 4;44(D1):D733-45, PMID:26553804; Cytometry B Clin Cytom 2009;76:375, PMID:19422053; Leukemia. 2005 May;19(5):750-8, PMID: 15759031, Brain Res 1995;697:235, PMID: 8593581; Neuroscience 2006;139:1467, PMID: 16580146; Virchows Arch 2002;441:605, PMID: 12461619;