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Encyclopedia > B cell

The abbreviation "B" comes from bursa of Fabricius that is an organ in birds in which avian B cells mature. The principal function of B cells is to make antibodies against soluble antigens. B cells are an essential component of the adaptive immune system. In birds, the bone marrow is the site of hematopoiesis and the bursa of Fabricius (Latin: Bursa cloacalis or Bursa fabricii) is a specialized organ that, as first demonstrated by Bruce Glick and later by Max Cooper and Robert Good, is necessary for B cell development. ... Drawing of the structure of cork as it appeared under the microscope to Robert Hook from Micrographia which is the origin of the word cell. POOP Cells in culture, stained for keratin (red) and DNA (green). ... Each antibody binds to a specific antigen; an interaction similar to a lock and key. ... An antigen is a molecule that stimulates an immune response. ... The immune system is the collection of organs and tissues involved in the adaptive defense of a body against foreign biological material. ...

Contents

Development of B cells

B cells are produced in the bone marrow of most mammals. Rabbits are an exception; their B cells develop in the appendix-sacculus rotundus. B cell development occurs through several stages, each stage representing a change in the genome content at the antibody loci. An antibody is composed of two light (L) and two heavy (H) chains, and the genes specifying them are found in the 'H' chain locus and the 'L' chain locus. In the H chain loci there are three regions, V, D and J, which recombine randomly, in a process called VDJ recombination, to produce a unique variable domain in the immunoglobulin of each individual B cell. Similar rearrangements occur for L chain locus except there are only two regions, namely V and J. The list below describes the process of immunoglobulin formation at the different stages of B cell development. Grays Anatomy illustration of cells in bone marrow. ... Genera Pentalagus Bunolagus Nesolagus Romerolagus Brachylagus Sylvilagus Oryctolagus Poelagus Rabbits are small mammals in the family Leporidae of the order Lagomorpha, found in several parts of the world. ... The word locus (plural loci) is Latin for place. In biology, a locus is the position of a gene (or other significant sequence) on a chromosome. ... Short and long arms Chromosome. ... Short and long arms Chromosome. ... // VDJ recombination VDJ recombination is a mechanism of DNA recombination used by humans and other vertebrates for protection against attacks by bacterial, viral, and parasitic invaders. ... Schematic of antibody binding to an antigen An antibody is a protein complex used by the immune system to identify and neutralize foreign objects like bacteria and viruses. ...

  • Progenitor B cells - Contains Germline H genes, Germline L genes
  • Early Pro-B cells - undergoes D-J rearrangement on the H chains
  • Late Pro-B cells - undergoes V-DJ rearrangement on the H chains
  • Large Pre-B cells - the H chain is VDJ rearranged, Germline L genes
  • Small Pre-B cells - undergoes V-J rearrangement on the L chains
  • Immature B cells - VJ rearranged on L chains, VDJ rearranged on H chains. There is start of expression of IgM receptors.
  • Mature B cells - There is start of expression of IgD

When the B cell fails in any step of the maturation process, it will die by a mechanism called apoptosis. If it recognizes self-antigen during the maturation process, the B cell will become suppressed (known as anergy) or undergo apoptosis. B cells are continuously produced in the bone marrow, but only a small portion of newly made B cells survive to participate in the long-lived peripheral B cell pool. Germline is a word used in biology and genetics. ... A cell undergoing apoptosis. ... Anergy is a theory in immunobiology in which there is a lack of reaction by the bodys defence mechanisms when foreign substances come into contact with the body. ...


Functions

The human body makes millions of different types of B cells each day that circulate in the blood and lymph performing the role of immune surveillence. They do not produce antibodies until they become fully activated. Each B cell has a unique receptor protein (referred to as the B cell receptor (BCR)) on its surface that will bind to one particular antigen. The BCR is a membrane-bound immunoglobulin, and it is this molecule that allows the distinction of B cells from other types of lymphocyte, as well as being the main protein involved in B cell activation. Once a B cell encounters its cognate antigen and receives an additional signal from a T helper cell, it can further differentiate into one of the two types of B cells listed below. The B cell may either become one of these cell types directly or it may undergo an intermediate differentiation step, the germinal center reaction, where the B cell will hypermutate the variable region of its immunoglobulin gene and possibly undergo class switching. Human blood smear: a - erythrocytes; b - neutrophil; c - eosinophil; d - lymphocyte. ... In mammals including humans, the lymphatic vessels (or lymphatics) are a network of thin tubes that branch, like blood vessels, into tissues throughout the body. ... Lymphocyte (stained) A lymphocyte is a type of white blood cell involved in the human bodys immune system. ... Schematic of antibody binding to an antigen An antibody is a protein complex used by the immune system to identify and neutralize foreign objects like bacteria and viruses. ... This article or section does not cite its references or sources. ... Germinal centers (GC) are an important part of the humoral immune response. ... This article needs to be cleaned up to conform to a higher standard of quality. ... Schematic of antibody binding to an antigen An antibody is a protein complex used by the immune system to identify and neutralize foreign objects like bacteria and viruses. ... For a non-technical introduction to the topic, see Introduction to Genetics. ... Immunoglobulin class switching (or isotype switching) is a biological mechanism that changes an antibody from one class to another, for example, from an isotype called IgM to an isotype called IgG. During this process, the constant region portion of the antibody heavy chain is changed, but the variable region of...


B cell types

A plasma cell
A plasma cell
  • Plasma B cells (also known as plasma cells) are large B cells that have been exposed to antigen and are producing and secreting large amounts of antibodies, which assist in the destruction of microbes by binding to them and making them easier targets for phagocytes and activation of the complement system. They are sometimes referred to as antibody factories. An electron micrograph of these cells reveals large amounts of rough endoplasmic reticulum, responsible for synthesizing the antibody, in the cell's cytoplasm.
  • Memory B cells are formed from activated B cells that are specific to the antigen encountered during the primary immune response. These cells are able to live for a long time, and can respond quickly following a second exposure to the same antigen.
  • B-1 cells express IgM in greater quantities than IgG and its receptors show polyspecificity, meaning that they have low affinities for many different antigens, but have a preference for other immunoglobulins, self antigens and common bacterial polysaccharides. B-1 cells are present in low numbers in the lymph nodes and spleen and are instead found predominantly in the peritoneal and pleural cavities.
  • B-2 cells are the conventional B cells most texts refer to.

Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Plasma cells are B lymphocytes that secrete immunoglobulins (antibodies). ... Each antibody binds to a specific antigen; an interaction similar to a lock and key. ... A microorganism or microbe is an organism that is so small that it is microscopic (invisible to the naked eye). ... A phagocyte is a cell that ingests and destroys foreign matter such as microorganisms or debris via a process known as phagocytosis. ... A complement protein attacking an invader. ... An electron micrograph is a micrograph made with an electron microscope. ... The endoplasmic reticulum or ER (endoplasmic means within the cytoplasm, reticulum means little net) is an organelle found in all eukaryotic cells. ... It has been suggested that Cytoplast be merged into this article or section. ... Memory B cells are a B cell sub-type that are formed following primary infection. ... This article does not cite any references or sources. ...

Recognition of antigen by B cells

A critical difference between B cells and T cells is how each lymphocyte "sees" its antigen. B cells recognize their cognate antigen in its native form. They recognize free (soluble) antigen in the blood or lymph using their BCR or membrane bound-immunoglobulin. In contrast, T cells recognize their cognate antigen in a processed form, as a peptide fragment presented by an antigen presenting cell's MHC molecule to the T cell receptor. T cells are a subset of lymphocytes that play a large role in the immune response. ... An antigen is a molecule that stimulates an immune response. ... Peptides (from the Greek πεπτος, digestible), are the family of short molecules formed from the linking, in a defined order, of various α-amino acids. ... An antigen presenting cell (APC) is a cell that displays foreign antigen complexed with MHC on its surface. ... MHC I (1hsa) vs MHC II (1dlh) (more details. ... The T cell receptor or TCR is responsible for recognizing antigen bound to Major histocompatibility complex (MHC). ...

Mechanism of action.
Mechanism of action.

Image File history File links Size of this preview: 390 × 599 pixelsFull resolution (651 × 1000 pixel, file size: 209 KB, MIME type: image/png) File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Image File history File links Size of this preview: 390 × 599 pixelsFull resolution (651 × 1000 pixel, file size: 209 KB, MIME type: image/png) File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ...

Activation of B cells

B cell recognition of antigen is not the only element necessary for B cell activation (a combination of clonal proliferation and terminal differentiation into plasma cells). B cells that have not been exposed to antigen, also known as Naive B cells, can be activated in a T-cell dependent or independent manner. The word proliferation can refer to: Nuclear proliferation Chemical weapon proliferation the spread in use of other weapons systems Cell proliferation According to Gloria Anzaldúa (1990), the difference between appropriation and proliferation is that the first steals and harms; the second helps heal breaches of knowledge. ... Differentiation can mean the following: In biology: cellular differentiation; evolutionary differentiation; In mathematics: see: derivative In cosmogony: planetary differentiation Differentiation (geology); Differentiation (logic); Differentiation (marketing). ... Plasma cells (also called plasma B cells or plasmocytes) are cells of the immune system that secrete large amounts of antibodies. ...


T-cell dependent activation

When a B cell ingests a pathogen, it attaches parts of the pathogen's proteins to a class II MHC protein. This complex is moved to the outside of the cell membrane, where it can be recognized by a T lymphocyte, which is compatible with similar structures on the cell membrane of a B lymphocyte. If the B cell and T cell structures match, the T lymphocyte activates the B lymphocyte, which produces antibodies against the bits of pathogen, called antigen, it has presented on its surface. A pathogen or infectious agent is a biological agent that causes disease or illness to its host. ... MHC I (1hsa) vs MHC II (1dlh) (more details. ... T cells are a subset of lymphocytes that play a large role in the immune response. ... B cells are lymphocytes that play a large role in the humoral immune response (as opposed to the cell-mediated immune response). ...


Most antigens are T-dependent, meaning T cell help is required for maximal antibody production. With a T-dependent antigen, the first signal comes from antigen cross linking the B cell receptor (BCR) and the second signal comes from co-stimulation provided by a T cell. T dependent antigens contain proteins that are presented on B cell Class II MHC to a special subtype of T cell called a Th2 cell. When a B cell processes and presents the same antigen to the primed Th cell, the T cell secretes cytokines that activate the B cell. These cytokines trigger B cell proliferation and differentiation into plasma cells. Isotype switching to IgG, IgA, and IgE and memory cell generation occur in response to T-dependent antigens. This isotype switching is known as Class Switch Recombination (CSR). Once this switch has occurred, that particular B-cell can no longer make the earlier isotypes, IgM or IgD. BCR may stand for one of the following: British Columbia Railway BCR gene Belarusian Central Rada, a puppet government of Belarus under German occupation during World War II Base Curve Radius, a parameter of a contact lens This is a disambiguation page — a navigational aid which lists other pages... During the activation of T cells, co-stimulation of molecules is often crucial to the development of an effective immune response. ... T cells are a subset of lymphocytes that play a large role in the immune response. ... The major histocompatibility complex (MHC) is a large genomic region or gene family found in most vertebrates containing many genes with important immune system roles. ... A T helper cell (sometimes also known as effector T cells or TH cells) are a group of lymphocytes (a type of white blood cell or leukocyte) that play a cornerstone role in establishing and maximising the ability of the immune system. ... Cytokines are a group of proteins and peptides that are used in organisms as signaling compounds. ... Plasma cells are B lymphocytes that secrete immunoglobulins (antibodies). ... Schematic of antibody binding to an antigen An antibody is a protein complex used by the immune system to identify and neutralize foreign objects like bacteria and viruses. ... IGA may stand for: Koji Igarashi, a video game producer Interactive genetic algorithm International Geothermal Association Independent Glass Association International Gothic Association International Gamers Award International Goat Association Irish Games Association Irish Geological Association ImmunoGlobulin A - see IgA nephritis which is a renal disease IGA (supermarkets) Independent Grocers Association or... IGE (Internet Gaming Entertainment) is the largest MMORPG services company world-wide, with offices in Los Angeles, Hong Kong, and Miami. ... IGM might be an acronym or abbreviation for: The polymeric immunoglobulin, IgM International Grandmaster, a chess ranking intergalactic medium Intragroup medium - see: Intracluster medium IG Metall - the dominant German metalworkers union IGM is an acronym created by Robinson Technologies for several early BBS door games, including Legend of the Red... Schematic of antibody binding to an antigen An antibody is a protein complex used by the immune system to identify and neutralize foreign objects like bacteria and viruses. ...


T-cell independent activation

Many antigens are T-independent, meaning they can deliver both of the signals to the B cell. Mice without a thymus (nude or athymic mice that do not produce any T cells) can respond to T-independent antigens. Many bacteria have repeating carbohydrate epitopes that stimulate B cells, through so called pattern recognition receptors, to respond with IgM synthesis in the absence of T cell help. There are two types of T-cell independent activation; Type 1 T cell-independent (polyclonal) activation, and type 2 T cell-independent activation (in which macrophages present several of the same antigen in a way that causes cross-linking of antibodies on the surface of B cells). Feral mouse A mouse (plural mice) is a rodent that belongs to one of numerous species of small mammals. ... Thymus, see Thyme. ... The word nude may refer to: The state of nudity. ... An epitope is the part of a foreign organism (or its proteins) that is being recognised by the immune system and targeted by antibodies, cytotoxic T cells or both. ... Pattern recognition receptors, or PRRs, are a class of cell surface receptors which are employed by the cells of the immune system to identify foreign (disease-associated) biomolecules in the body. ... Polyclonal antibodies are antibodies that are derived from different cell lines. ...


The ancestral roots of B cells

In an October 2006 issue of Nature Immunology, it was reported that certain B-cells of primitive vertebrates (like fish and amphibians) are capable of phagocytosis, a function usually associated with cells of the innate immune system. The authors of this article postulate that these phagocytic B-cells represent the ancestral history shared between macrophages and lymphocytes; B-cells may have evolved from macrophage-like cells during the formation of the adaptive immune system[1]. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Typical classes Petromyzontidae (lampreys) Placodermi - extinct Chondrichthyes (cartilaginous fish) Acanthodii - extinct Actinopterygii (ray-finned fish) Actinistia (coelacanths) Dipnoi (lungfish) Amphibia (amphibians) Reptilia (reptiles) Aves (birds) Mammalia (mammals) Vertebrata is a subphylum of chordates, specifically, those with backbones or spinal columns. ... A giant grouper at the Georgia Aquarium Fish are aquatic vertebrates that are typically cold-blooded; covered with scales, and equipped with two sets of paired fins and several unpaired fins. ... Subclasses and Orders    Order Temnospondyli - extinct Subclass Lepospondyli - extinct Subclass Lissamphibia    Order Anura    Order Caudata    Order Gymnophiona Amphibians (class Amphibia; from Greek αμφις both and βιος life) are a taxon of animals that include all living tetrapods (four-legged vertebrates) that do not have amniotic eggs, are ectothermic (term for the animals... Phagocytosis is a form of endocytosis wherein large particles are enveloped by the cell membrane of a (usually larger) cell and internalized to form a phagosome, or food vacuole. ... The innate immune system comprises the cells and mechanisms that defend the host from infection by other organisms, in a non-specific manner. ... Macrophages (Greek: big eaters) are cells found in tissues that are responsible for phagocytosis of pathogens, dead cells and cellular debris. ... A lymphocyte is a type of white blood cell involved in the human bodys immune system. ... The immune system is the collection of organs and tissues involved in the adaptive defense of a body against foreign biological material. ...


B cells in humans (and other vertebrates) are nevertheless able to endocytose antibody-fixed pathogens, and it is through this route that MHC Class II presentation by B cells is possible, allowing Th2 help and stimulation of B cell proliferation. This is purely for the benefit of MHC Class II presentation, not as a significant method of reducing the pathogen load.


References

  1. ^ J. Li, D.R. Barreda, Y.-A. Zhang, H. Boshra, A.E. Gelman, S. LaPatra, L. Tort & J.O. Sunyer (2006). "B lymphocytes from early vertebrates have potent phagocytic and microbicidal abilities". Nature Immunology 7: 1116–1124. PMID 16980980. 

See also

The process by which B-cells produce antibodies with increased affinity for antigen. ... Each antibody binds to a specific antigen; an interaction similar to a lock and key. ... The clonal selection theory has become a widely accepted model for how the immune system responds to infection and how certain types of B and T lymphocytes are selected for destruction of specific antigens invading the body. ... Original antigenic sin (first described in 1960 by Thomas Francis, Jr. ...

External links


  Results from FactBites:
 
B Cells and T Cells (1889 words)
B cells are not only produced in the bone marrow but also mature there.
T cells is to monitor all the cells of the body, ready to destroy any that express foreign antigen fragments in their class I molecules.
T cells bind an epitope consisting of an antigen fragment lying in the groove of a class II histocompatibility molecule.
B cell at AllExperts (675 words)
B cells are lymphocytes that play a large role in the humoral immune response (as opposed to the cell-mediated immune response).The abbreviation "B" stands for the bursa of Fabricius which is an organ unique to birds, where avian B cells mature.
B cells are produced through several stages, each stage represents a change in the genome content, in which the variety of antibodies are produced.
B cells are continuously produced in the bone marrow, but only a small portion of newly made B cells survive to participate a part in the long-lived peripheral B cell pool.
  More results at FactBites »

 
 

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