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Encyclopedia > Germinal center
Germinal center
Image labeled in German, but "Keimzentrum" visible in upper right.
Gray's subject #175 689
Dorlands/Elsevier c_20/12226657

Germinal centers (GC) are an important part of the humoral immune response. They develop dynamically after the activation of B-cells by T-dependent antigen. Histologically, the GCs describe microscopically distinguishable parts in lymphoid tissues. Image File history File linksMetadata No higher resolution available. ... Elseviers logo. ... Humoral immunity is the aspect of immunity that is mediated by secreted antibodies, produced in the cells of the B lymphocyte lineage (B cell). ... B cells are lymphocytes that play a large role in the humoral immune response (as opposed to the cell-mediated immune response). ... An antigen is a substance that stimulates an immune response, especially the production of antibodies. ... A thin section of lung tissue stained with hematoxylin and eosin. ... Wikipedia does not have an article with this exact name. ...

Contents

Process

1. Activated B-cells migrate into the follicular system and begin monoclonal expansion in the environment of follicular dendritic cells (FDC). Monoclonal antibodies (mAb) are antibodies that are identical because they were produced by one type of immune cell, all clones of a single parent cell. ... Dendritic cells (DC) are immune cells and form part of the mammalian immune system. ...


2. After three days of expansion the B cells mutate their antibody-encoding DNA and thus generate a diversity of clones in the germinal centre. This also involves deletions, insertions and recombination of the V, D, J genes. Each antibody binds to a specific antigen; an interaction similar to a lock and key. ... For other senses of the word code, see code (disambiguation). ... The structure of part of a DNA double helix Deoxyribonucleic acid (DNA) is a nucleic acid that contains the genetic instructions for the development and function of living organisms. ... Molecular cloning refers to the procedure of isolating a defined DNA sequence and obtaining multiple copies of it in vivo. ... Recombination usually refers to the biological process of genetic recombination and meiosis, a genetic event that occurs during the formation of sperm and egg cells. ... V(D)J recombination is a mechanism of DNA recombination used by humans and other vertebrates for immunological protection against attacks by bacterial, viral, and parasitic invaders. ...


3. Upon some unidentified stimulus from the FDC, the B cells start to expose their antibody to their surface and in this stage are referred to as centrocytes. The centrocytes are in a state of activated apoptosis and compete for survival signals from FDCs that present the antigen. This rescue process is believed to be dependent on the affinity of the antibody to the antigen. Activation Activation in science generally refers to prepare some object for a process. ... A cell undergoing apoptosis. ... Look up affinity in Wiktionary, the free dictionary. ...


4. The functional B-cells have then to interact with helper T cells to get final differentiation signals. This also involves isotype switching for example from IgM to IgG. The interaction with T cells is believed to prevent the generation of autoreactive antibodies.[1] 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. ...


5. The B cells become either a plasma cell spreading antibodies or a memory B cell that will be activated in subsequent contacts with the same antigen. They may also restart the whole process of proliferation, mutation and selection according to the recycling hypothesis. Plasma cells (also called plasma B cells or plasmocytes) are cells of the immune system that secrete large amounts of antibodies. ... Memory B cells are a B cell sub-type that are formed following primary infection. ... 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. ... It has been suggested that mutant be merged into this article or section. ... Selection is hierachically classified into natural and artificial selection. ...


Morphology at different stages

The morphology of GCs is very specific and shows properties which are characteristic for different stages of the reaction. The term morphology in biology refers to the outward appearance (shape, structure, colour, pattern) of an organism or taxon and its component parts. ...

  • In an early state of the reaction a network of FDCs is fully filled with proliferating B cells.
  • Later at day 4 of the reaction GCs show a separation of two zones, the dark and the light zone.[2] The former still contains dominantly proliferating cells while the latter one is the area of B cells selection.
  • These zones dissolve after 10 days of GC development which ends after about 3 weeks.

References

  1. ^ Thorbecke GJ, Amin AR, Tsiagbe VK (1994). "Biology of germinal centers in lymphoid tissue". FASEB 8: 832-840. PMID 8070632. 
  2. ^ Meyer-Hermann ME (2002). "A Mathematical Model for the Germinal Center Morphology and Affinity Maturation". J. theor. Biol. 216: 273-300. PMID 12183119. 

See also

Lymph nodes are components of the lymphatic system. ...

External links


  Results from FactBites:
 
Hematopathology: Reactive Lymph Nodes (650 words)
The germinal centers also demonstrate abundant mitotic figures and so-called "tingible-body macrophages".
The B-cells that survive the tumultuous, Darwinian struggle within the germinal center eventually differentiate into plasma cells.
Germinal centers appear about a week after the node is challenged by an immunogenic antigen and gradually subside unless further challenged.
Implications for affinity maturation in the germinal centers (838 words)
Implications for affinity maturation in the germinal centers
From this one-pass selection model of the germinal center reaction, with the many variants I analyzed, it is clear that the observed numbers of high affinity cells can only be generated if mutant cells are selected and amplified very often during the germinal center reaction.
If the rare high affinity mutants are to dominate the germinal centers, assuming that they do not readily leave the germinal centers, it is necessary that almost all germline cells die.
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