A reference guide to centroblasts — the rapidly dividing dark-zone B cells of the germinal center — covering somatic hypermutation, affinity maturation, B-cell development and the lymphomas that arise from germinal center B cells.
Key references: Victora GD, Nussenzweig MC. Germinal centers. Annual Review of Immunology 2022;40:413–442 · National Cancer Institute, Adult Non-Hodgkin Lymphoma Treatment (PDQ®) – Health Professional Version. Figures above are approximate values reported in the literature. Educational information only, not medical advice.
The rapidly dividing B cells that drive antibody affinity maturation
Centroblasts are large, rapidly proliferating B lymphocytes found in the dark zone of germinal centers within secondary lymphoid organs such as lymph nodes, spleen, and Peyer's patches. They represent a critical stage in the adaptive immune response, where B cells undergo somatic hypermutation (SHM) of their immunoglobulin variable region genes, generating a diverse repertoire of antibody variants with potentially higher affinity for the invading pathogen.
The germinal center reaction is one of the most remarkable processes in immunology. When a naive B cell encounters its cognate antigen and receives T cell help (through CD40-CD40L interaction and cytokine signals), it migrates to a lymphoid follicle and begins the germinal center reaction. Within the dark zone, the B cell transforms into a centroblast -- a large, highly mitotic cell with dispersed chromatin and minimal surface immunoglobulin expression. Centroblasts divide every 6-12 hours, making them among the most rapidly proliferating cells in the human body.
During this rapid proliferation, the enzyme Activation-Induced Cytidine Deaminase (AID) introduces point mutations into the variable regions of the immunoglobulin heavy and light chain genes at a rate approximately one million times higher than the background mutation rate. This process, known as somatic hypermutation, is the engine of antibody affinity maturation -- the progressive improvement in antibody binding strength over the course of an immune response.
Understanding centroblast biology is clinically important because many B-cell lymphomas arise from germinal center B cells. Diffuse large B-cell lymphoma (DLBCL), the most common type of non-Hodgkin lymphoma, includes a germinal center B-cell-like subtype that originates from centroblasts. Burkitt lymphoma also derives from germinal center B cells and is characterized by a translocation that places the MYC oncogene under the control of immunoglobulin gene regulatory elements.
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