B-lymphocyte-specific membrane protein that plays a role in the regulation of cellular calcium influx necessary for the development, differentiation, and activation of B-lymphocytes (PubMed:3925015, PubMed:7684739, PubMed:12920111). Functions as a store-operated calcium (SOC) channel component promoting calcium influx after activation by the B-cell receptor/BCR (PubMed:7684739, PubMed:12920111, PubMed:18474602). Forms homotetramers (PubMed:7684739, PubMed:18474602). Interacts with the heavy and light chains of cell surface IgM, the antigen-binding components of the BCR (PubMed:18474602). Constitutively associated with membrane rafts. Expressed on B-cells. Phosphorylated on serines and threonines in resting B-cells. Protein kinase C/PKC can use CD20 as substrate. The disease is caused by variants affecting the gene represented in this entry. Monoclonal antibodies (mAb) against CD20 are used to treat B-cell non-Hodgkin lymphoma (NHL). These antibodies include Rituximab (Mabthera), Britumomab (Zevalin) and Tositumomab (Bexxar). CD20 engaged by mAb can generate transmembrane signals capable of directly controlling cell growth and triggering cell death in certain tumors. Alternatively, mAb can mediate complement-dependent cytotoxicity. Belongs to the MS4A family. Epitope 1, mapped in PubMed:16785532, is predicted to be buried in the membrane. Its accessibility to the extracellular space, and thus to antibody recognition, is not explained. CD20 entry