Germinal center

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Germinal center
Germinal center of a lymph node showing proliferation and development stages of a B cell.
Identifiers
MeSH	D018858
Anatomical terminology [edit on Wikidata]

Germinal centers or germinal centres (GCs) are transiently formed structures within B cell zone (follicles) in secondary lymphoid organs – lymph nodes, ileal Peyer's patches, and the spleen^[1] – where mature B cells are activated, proliferate, differentiate, and mutate their antibody genes (through somatic hypermutation aimed at achieving higher affinity) during a normal immune response; most of the germinal center B cells (B_GC) are removed by tingible body macrophages.^[2] There are several key differences between naive B cells and GC B cells, including level of proliferative activity, size, metabolic activity and energy production.^[3] The B cells develop dynamically after the activation of follicular B cells by T-dependent antigen. The initiation of germinal center formation involves the interaction between B and T cells in the interfollicular area of the lymph node, CD40-CD40L ligation, NF-kB signaling and expression of IRF4 and BCL6.^[4]

GC B cells cycle through the two distinct zones of the germinal center: the light zone and the dark zone.^[3][4][5][6] As they undergo rapid and mutative cellular division, B cells of the germinal center's dark zone are known as centroblasts. Once these B cells have stopped proliferating in the dark zone and moved to the light zone, they are known as centrocytes, and are subjected to selection by follicular helper T (T_FH) cells in the presence of follicular dendritic cells (FDCs).^[3][4][5][6] There are three possible fates for GC B cells that have been positively selected in the light zone: plasma cell, memory B cell or B cell licensed to return to the dark zone for proliferation and mutation.^[4][6] These three fates are achieved via the distinct mechanisms described below. Germinal centers are an important part of the B cell humoral immune response, acting as central factories for the generation of affinity matured B cells specialized in producing improved antibodies that effectively recognize antigen (e.g. infectious agents), and for the production of long-lived plasma cells and durable memory B cells.