Immunology Terms Starting With B
Immunology Glossary: B
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B Cell
/ BEE sel / · B for bursa of Fabricius (in birds) or Bone marrow (in mammals)
B Cell is a lymphocyte that matures in the bone marrow and produces antibodies that drive humoral immunity and long-term immunological memory.
B cells express unique B cell receptors formed by somatic recombination of immunoglobulin gene segments, with each receptor recognizing a distinct antigen. Upon antigen binding and receiving co-stimulatory signals from helper T cells, these lymphocytes proliferate and differentiate into antibody-secreting plasma cells or long-lived memory B cells. Germinal centers in lymph nodes are the sites of somatic hypermutation and affinity maturation, processes that progressively increase antibody binding strength over the course of an immune response.
A single human can generate an estimated 10 billion distinct B cell receptor specificities through this combinatorial gene rearrangement.
During the germinal center reaction, B cells that acquire mutations improving antigen binding are selectively retained while lower-affinity cells undergo apoptosis. This Darwinian selection process, first described in detail by César Milstein and colleagues in the 1970s and 1980s, can increase antibody affinity by 10,000-fold or more over the course of an infection.
Immune System Fun Facts →B cells produce strong antibody responses immediately upon first encountering an antigen. Naive B cells require activation, T cell help, and germinal center maturation before generating high-affinity antibodies, a process that takes one to two weeks.
After yellow fever vaccination, B cells in the draining lymph nodes undergo germinal center reactions that generate high-affinity IgG antibodies. Protective antibody titers can persist for more than 10 years following a single dose of the yellow fever vaccine.
B Lymphocyte
/ bee LIM-foh-syt / · B for bone marrow + Latin lympha (water) + Greek kytos (cell)
B Lymphocyte is a white blood cell of the adaptive immune system that differentiates from bone marrow progenitors, expresses antigen-specific surface immunoglobulin, and produces antibodies upon activation.
B lymphocytes and T lymphocytes are the two main classes of adaptive immune cells, together forming the cellular basis of antigen-specific immunity. During affinity maturation in germinal centers, somatic hypermutation introduces point mutations into immunoglobulin variable regions at a rate roughly one million times higher than the background mutation rate of the genome, and B cells with improved antigen binding are selectively expanded. Class switch recombination then changes the antibody heavy chain constant region from IgM to IgG, IgA, or IgE, directed by cytokine signals that tailor the antibody class to the nature of the threat.
B lymphocytes take their name from the bursa of Fabricius, a lymphoid organ found only in birds (class Aves) where this cell lineage was first identified by Robert Good and colleagues in the early 1960s. In humans and other mammals, the bone marrow performs the equivalent developmental function, but the "B" designation has been retained in honor of that original discovery.
B lymphocytes and B cells are separate cell types. They are two names for the same major lymphocyte lineage, distinguished only by context or convention.
In chickens (Gallus gallus domesticus), B lymphocytes develop in the bursa of Fabricius, a pouch-like organ near the cloaca. Surgical removal of the bursa in chick embryos before hatching eliminates most antibody production, leaving the birds unable to mount normal humoral immune responses during the first weeks of life.
Basophil
/ BAY-soh-fil / · Greek basis (base) + philein (to love)
Basophil is a rare circulating granulocyte that stains with basic dyes, degranulates to release histamine and other mediators upon IgE receptor crosslinking, and drives allergic inflammation and anti-parasite immunity.
Basophils constitute less than one percent of circulating white blood cells but are potent amplifiers of allergic responses through rapid degranulation when surface-bound IgE is crosslinked by allergen. These cells also produce cytokines including IL-4 and IL-13 that promote the Th2 immune environment required for IgE class switching in B cells, establishing a positive feedback loop that sustains allergic sensitization. Unlike mast cells, which reside permanently in tissues, basophils circulate in blood and enter inflamed tissues only during active allergic reactions.
Each basophil granule contains preformed histamine, heparin, and proteases that are released within seconds of receptor crosslinking.
Basophils were long considered immunological bystanders, but studies in mice published around 2009 by groups including those of Minoru Asada and David Artis demonstrated that basophils can migrate to lymph nodes and directly promote IgE production by B cells, a function previously attributed only to T helper cells.
Basophils and mast cells are identical cell types with different names. They share some surface receptors and mediators but differ in their developmental origin, tissue distribution, lifespan, and granule composition.
During allergic responses to house dust mite (Dermatophagoides pteronyssinus) allergens, basophils in sensitized individuals degranulate within minutes of allergen exposure. A single basophil can release enough histamine to measurably dilate nearby capillaries, contributing to the wheal-and-flare reaction visible within 15 minutes on a skin prick test.
Immune System Fun Facts →