germinal centers

WordNet

1. of or belonging to neither the right nor the left politically or intellectually
2. a building dedicated to a particular activity; "they were raising money to build a new center for research" (同)centre
3. (American football) the position of the player on the line of scrimmage who puts the ball in play; "it is a centers responsibility to get the football to the quarterback"
4. a position on a basketball team of the player who participates in the jump that starts the game
5. the position on a hockey team of the player who participates in the face off at the beginning of the game
6. a place where some particular activity is concentrated; "they received messages from several centers" (同)centre
7. the sweet central portion of a piece of candy that is enclosed in chocolate or some other covering (同)centre
8. the object upon which interest and attention focuses; "his stories made him the center of the party" (同)centre, center of attention, centre of attention
9. an area that is approximately central within some larger region; "it is in the center of town"; "they ran forward into the heart of the struggle"; "they were in the eye of the storm" (同)centre, middle, heart, eye
10. a point equidistant from the ends of a line or the extremities of a figure (同)centre, midpoint
11. a cluster of nerve cells governing a specific bodily process; "in most people the speech center is in the left hemisphere" (同)centre, nerve_center, nerve centre
12. (football) the person who plays center on the line of scrimmage and snaps the ball to the quarterback; "the center fumbled the handoff" (同)snapper
13. (basketball) the person who plays center on a basketball team
14. (ice hockey) the person who plays center on a hockey team
15. politically moderate persons; centrists
16. the middle of a military or naval formation; "they had to reinforce the center"
17. move into the center; "That vase in the picture is not centered" (同)centre
18. equally distant from the extremes (同)halfway, middle, midway
19. containing seeds of later development; "seminal ideas of one discipline can influence the growth of another" (同)originative, seminal
20. (American football) putting the ball in play by passing it (between the legs) to a back; "the quarterback fumbled the snap" (同)snap
21. seventh month of the Revolutionary calendar (March and April); the month of buds

PrepTutorEJDIC

1. 芽の,胚(はい)種の / (発達の)初期段階の;原始の

Wikipedia preview

出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2018/02/05 12:36:54」(JST)

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Germinal center
Germinal center of a lymph node showing proliferation and development stages of a B cell .
Dorlands /Elsevier	c_20/12226657
Anatomical terminology

Germinal centers or germinal centres (GCs) are sites within secondary lymphoid organs – lymph nodes and the spleen where mature B cells proliferate, differentiate, and mutate their antibody genes (through somatic hypermutation aimed at achieving higher affinity), and switch the class of their antibodies (for example from IgM to IgG) during a normal immune response to an infection. They develop dynamically after the activation of follicular B cells by T-dependent antigen.

As they undergo rapid and mutative cellular division in the dark zone, B cells of the germinal center are known as centroblasts. Once these B cells have stopped proliferating, they migrate to the light zone where 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). 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 infectious agents, and for the production of durable memory B cells. Histologically, the GCs describe microscopically distinguishable parts in lymphoid tissues.

Process

1. Within lymph nodes, mature peripheral B cells known as follicular (Fo) B cells acquire antigen from follicular dendritic cells (FDCs) and in turn present it to cognate CD4+ T_FH cells at the border that demarcates the T cell zone and B cell follicles (also known as lymphoid follicles). During T_FH-B cell conjugation, the B cell receives critical signals to undergo isotype switching (also called immunoglobulin class switching) and to commence monoclonal expansion. During this time they are referred to as centroblasts and make up the dark zone.
2. After several rounds of cellular division, the B cells go through somatic hypermutation, a process by which they mutate their antibody-encoding DNA and thus generate a diversity of clones in the germinal center. This involves pseudo-random substitutions biased towards regions encoding the antigen recognition surface of the antibodies the B cells produce. This phenomenon underscores the process of affinity maturation, whereby greater affinity antibodies are produced and selected for after antigen recognition.
3. Upon receiving an unidentified stimulus, the maturing B cells (centroblasts) migrate from the dark zone to the light zone and start to express their antibody on the cell surface and at this stage are referred to as centrocytes. The centrocytes are in a state of activated apoptosis and compete for survival signals derived from follicular dendritic cell and T_FH cells. This rescue process, known as germinal center selection, is believed to be dependent on the affinity of their surface antibody to the antigen. Such that, a B cell that has successfully gained mutations that confer a higher affinity surface antibody towards antigen gains a survival advantage over lower affinity B cell clones and those that have gained deleterious mutations. Cyclic re-entry into the dark zone once again as centroblasts allows a chance for otherwise non-selected B cell mutants to gain more mutations in order to improve affinity towards antigen. Interactions with T cells are also believed to prevent the generation of autoreactive germinal center B cells.
4. At some unclear stage of their centroblast-centrocyte cycling, maturing B cells receive a final differentiation signal to exit the germinal center as an antibody producing plasma cell which are cells that secrete large quantities of antibody or a memory B cell that can be reactivated in subsequent contacts with the same antigen. Selected B cells may also restart the whole cycle of mutative centroblast division and centrocyte selection. In this way the adaptive immune system, in part through these germinal center reactions, can gradually better recognize antigens over time.

Morphology at different stages

The morphology of GCs is very specific and shows properties which are characteristic for different stages of the reaction.

• 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. The former still contains dominantly proliferating and mutating B cells while the latter one is the area of B cell selection.
• These zones dissolve after 10 days of GC development which ends after about 3 weeks.

Medical relevance

As germinal centers are important structures of the adaptive immune system, their deregulation is implied in many immune diseases, for example rheumatoid arthritis, immunodeficiency and many lymphomas like DLBCL and Burkitt's lymphoma.

See also

• Lymphatic system
• Tingible body
• Mantle zone

External links

• UIUC Histology Subject 563
• Histology image: 07103loa – Histology Learning System at Boston University - "Lymphoid Tissues and Organs: lymph node, germinal centre"
• Hyperlinked Human Histology
• MedEd at Loyola Histo/practical/lymph/hp12-42.html

UpToDate Contents

全文を閲覧するには購読必要です。 To read the full text you will need to subscribe.

• 1. Prognosis of diffuse large B cell lymphoma
• 2. 体液性免疫応答 the humoral immune response
• 3. 進行期びまん性大細胞型B細胞性リンパ腫の初期治療 initial treatment of advanced stage diffuse large b cell lymphoma
• 4. 造血腫瘍の分類 classification of the hematopoietic neoplasms
• 5. 非ホジキンリンパ腫の病理の概要 overview of the pathobiology of the non hodgkin lymphomas

English Journal

• CD137 Is Expressed in Follicular Dendritic Cell Tumors and in Classical Hodgkin and T-Cell Lymphomas: Diagnostic and Therapeutic Implications.

• Anderson MW, Zhao S, Freud AG, Czerwinski DK, Kohrt H, Alizadeh AA, Houot R, Azambuja D, Biasoli I, Morais JC, Spector N, Molina-Kirsch HF, Warnke RA, Levy R, Natkunam Y.SourceDepartment of Pathology, Stanford University School of Medicine, Stanford, California.
• The American journal of pathology.Am J Pathol.2012 Sep;181(3):795-803.
• CD137 (also known as 4-1BB and TNFRSF9) is a member of the tumor necrosis factor receptor superfamily. Originally identified as a costimulatory molecule expressed by activated T cells and NK cells, CD137 is also expressed by follicular dendritic cells, monocytes, mast cells, granulocytes, and endoth
• PMID 22901750

Japanese Journal

• Composite Follicular Lymphoma and CD5-Positive Nodal Marginal Zone Lymphoma

• Journal of Clinical and Experimental Hematopathology 56(1), 55-58, 2016
• NAID 130005158794

• 若年性節性濾胞辺縁帯リンパ腫の 2 例

• 日本臨床細胞学会雑誌 54(5), 335-340, 2015
• NAID 130005108761

Related Links

• Germinal center | definition of germinal center by Medical ...

Diffuse large B-cell lymphomas in immunocompetent patients, as determined by gene expression profiling and by immunophenotypic expression patterns, can be divided into clinically relevant groups: germinal center and activated B ...

• Germinal centers. - National Center for Biotechnology Information

1. Annu Rev Immunol. 1994;12:117-39. Germinal centers. MacLennan IC(1). Author information: (1)Department of Immunology, University of Birmingham Medical School, England. Germinal centers develop in the B cell ...

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★リンクテーブル★

関連記事	「center」「germinal」

「center」

　　[★]

• n.

• センター、中心、中央、中枢、中央に置く

関

central、centre、centro、centrum、hub、medial、middle

　 　 　 　 　 　 　 　 　 　 　 　 　 　 　 　 　 　

「germinal」

　　[★]

• 胚の

関

embryo、embryonic、germ