BCR and Autoimmunity: The lymphocytoid portion of the tumor cell clone typically expresses surface IgM in conjunction with pan B cell markers, including CD19 (a B cell receptor [BCR] coreceptor that decreases the threshold for antigen-dependent stimulation of BCR signaling), CD20 (a phosphoprotein that optimizes humoral immune responses to T-independent [TI] antigens), CD22 (a sialic acid-binding, immunoregulatory transmembrane lectin that prevents overactivation of the immune system and development of autoimmunity), and CD79a (an accessory component of the BCR known as Igα).