The 2H7 monoclonal antibody reacts with human and primate CD20. CD20 is a B cell-specific 33-37 kDa transmembrane protein which is also known as B-lymphocyte antigen, B1, and Bp35. CD20 plays roles in intracellular calcium regulation and B cell activation and is critical for an optimal B cell immune response against T-independent antigens. CD20 is first expressed after the induction of CD19 together with IgM during the pre-B to immature B cell transition in the bone marrow. It’s expression then increases during maturation with almost all mature B cells expressing some level of CD20. However, CD20 is not expressed by plasma blasts or plasma cells. CD20 is expressed by most B cell neoplasms, and is useful in diagnosing B cell lymphomas and leukemia. Many anti-CD20 monoclonal antibodies are currently being used to successfully treat leukemia, lymphomas, and various autoimmune diseases. The 2H7 monoclonal antibody has been shown to bind to an epitope in the large extracellular loop of human CD20.