Fig. 2.

B-cell maturation. B cells originate from common lymphoid progenitor (stem) cells in bone marrow. They first develop into pro-B cells, then differentiate into pre-B cells (at which point CD20 is expressed) and immature B cells through a process of rearrangements at the immunoglobulin locus which lead to surface expression of the pre-B cell receptor, and later a mature B-cell receptor capable of binding antigen. Immature B cells undergo a selection process to prevent development of self-reactivity. They then migrate out of the bone marrow into the periphery (lymph nodes and spleen), where they become mature naïve B cells. Binding to cognate antigen triggers development of antigen-specific mature activated B cells, which become either plasmablasts and antibody-secreting plasma cells (CD20-) or remain memory B cells (CD20+). CD cluster of differentiation, CSF cerebrospinal fluid, HLA human leukocyte antigen, Ig immunoglobulin