Figure 1.

B cell development stages. B cells develop in the bone marrow from haematopoietic stem cells (HSCs), progressing from pro-B cell stages to pre-B cells before migrating into the circulation as transitional B cells. Upon antigen recognition, activated B cells migrate to secondary lymphoid organs and enter germinal centres where they undergo clonal expansion and somatic hypermutation (SHM) within the dark zones (DZ). B cells with disadvantageous mutations die by apoptosis whereas those B cells with improved receptor affinity interact with follicular dendritic cells (FDC) and T follicular helper cells (TFH), in the light zone (LZ). B cells undergo class switch recombination (CSR) and receive survival signals to differentiate into memory B cells and long-lived plasma cells (PCs) (5). Naïve B cells can differentiate into short-lived plasma cells through extrafollicular responses (6). Naïve B cells can also differentiate into age-associated B cells (ABCs) upon stimulation (7).