WordNet

flog with or as if with a flexible rod
make a shift in or exchange of; "First Joe led; then we switched" (同)change over, shift
control consisting of a mechanical or electrical or electronic device for making or breaking or changing the connections in a circuit (同)electric switch, electrical switch
the act of changing one thing or position for another; "his switch on abortion cost him the election" (同)switching, shift
a basketball maneuver; two defensive players shift assignments so that each guards the player usually guarded by the other
a flexible implement used as an instrument of punishment
hairpiece consisting of a tress of false hair; used by women to give shape to a coiffure
railroad track having two movable rails and necessary connections; used to turn a train from one track to another or to store rolling stock
lay aside, abandon, or leave for another; "switch to a different brand of beer"; "She switched psychiatrists"; "The car changed lanes" (同)shift, change
elegance in dress or behavior; "she has a lot of class"
a collection of things sharing a common attribute; "there are two classes of detergents" (同)category, family
a league ranked by quality; "he played baseball in class D for two years"; "Princeton is in the NCAA Division 1-AA" (同)division
a body of students who are taught together; "early morning classes are always sleepy" (同)form, grade, course
people having the same social, economic, or educational status; "the working class"; "an emerging professional class" (同)stratum, social_class, socio-economic class
a body of students who graduate together; "the class of 97"; "she was in my year at Hoehandle High" (同)year
(biology) a taxonomic group containing one or more orders

PrepTutorEJDIC

(特にむち打ち用の)『しなやかな小枝』(棒) / (しなやかな小枝・棒などで)むち打つこと / (…における)『変更』《+in+名》;(…から…への)転換《+from+名+to+名》 / (電気の)『スイッチ』,開閉器 / (電話の)交換台 / (鉄道の)転てつ器,ポイント / (女性の髪用の)入れ毛,かもじ / 〈人・動物〉‘を'むちで打つ,むち打つ(whip) / 〈むちなど〉‘を'振る,(むちを打つように)…‘を'さっと振る / (…に)…‘を'『転換する,』変更する《+名+to+名(doing)》 / …‘を'交換する(exchange) / 〈線路のポイント〉‘を'転換する,転てつする / (ある方向・進路に)変わる,転じる,移る《+to(into)+名》 / 交換する,取り替える
〈C〉(何らかの類似性を持つ)(…の)『種類』,類(sort, kind)《+『of』+『名』》 / 〈C〉《集合的に》《単数扱い》『クラス』,学級,組 / 〈U〉〈C〉(クラス単位の)『授業』;授業時間 / 〈C〉《米》《集合的に》(主に高校・大学の)同期生 / 〈C〉《しばしば複数形で》(同程度の教育・経済力・社会的地位などを持つ)『階級』,階層 / 〈C〉(交通機関などの)『等級』 / 〈C〉(英国の大学の)試験の合格等級 / 〈C〉綱(こう)(動植物の分類で門(phylum, division)と目(もく)(order)の間) / 〈U〉《話》(その人の社会的地位を高く見せる)風格 / …'を'(…の)部類に入れる《+『名』+『among』(『with』)+『名』》,(…として)…'を'分類する《+『名』+『as』+『名』》

Wikipedia preview

出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2013/11/20 02:32:58」(JST)

wiki en

Mechanism of class switch recombination that allows isotype switching in activated B cells

Immunoglobulin class switching (or isotype switching or isotypic commutation or class switch recombination(CSR)) is a biological mechanism that changes a B cell's production of 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 the heavy chain stays the same (the terms "variable" and "constant" refer to changes or lack thereof between antibodies that target different epitopes). Since the variable region does not change, class switching does not affect antigen specificity. Instead, the antibody retains affinity for the same antigens, but can interact with different effector molecules.

Mechanism[edit]

Class switching occurs after activation of a mature B cell via its membrane-bound antibody molecule (or B cell receptor) to generate the different classes of antibody, all with the same variable domains as the original antibody generated in the immature B cell during the process of V(D)J recombination, but possessing distinct constant domains in their heavy chains.^[1]

Naïve mature B cells produce both IgM and IgD, which are the first two heavy chain segments in the immunoglobulin locus. After activation by antigen, these B cells proliferate. If these activated B cells encounter specific signaling molecules via their CD40 and cytokine receptors (both modulated by T helper cells), they undergo antibody class switching to produce IgG, IgA or IgE antibodies. During class switching, the constant region of the immunoglobulin heavy chain changes but the variable regions, and therefore antigenic specificity, stay the same. This allows different daughter cells from the same activated B cell to produce antibodies of different isotypes or subtypes (e.g. IgG1, IgG2 etc.).^[2]

The order of the heavy chain exons are as follows:

μ - IgM
δ - IgD
γ3 - IgG3
γ1 - IgG1
pseudogene similar to ε gene that is not used
α1 - IgA1
γ2 - IgG2
γ4 - IgG4
ε - IgE
α2 - IgA2^{[citation needed]}

Class switching occurs by a mechanism called class switch recombination (CSR) binding. Class switch recombination is a biological mechanism that allows the class of antibody produced by an activated B cell to change during a process known as isotype or class switching. During CSR, portions of the antibody heavy chain locus are removed from the chromosome, and the gene segments surrounding the deleted portion are rejoined to retain a functional antibody gene that produces antibody of a different isotype. Double-stranded breaks are generated in DNA at conserved nucleotide motifs, called switch (S) regions, which are upstream from gene segments that encode the constant regions of antibody heavy chains; these occur adjacent to all heavy chain constant region genes with the exception of the δ-chain. DNA is nicked and broken at two selected S-regions by the activity of a series of enzymes, including Activation-Induced (Cytidine) Deaminase (AID), uracil DNA glycosylase and apyrimidic/apurinic (AP)-endonucleases.^[3]^[4] The intervening DNA between the S-regions is subsequently deleted from the chromosome, removing unwanted μ or δ heavy chain constant region exons and allowing substitution of a γ, α or ε constant region gene segment. The free ends of the DNA are rejoined by a process called non-homologous end joining (NHEJ) to link the variable domain exon to the desired downstream constant domain exon of the antibody heavy chain.^[5] In the absence of non-homologous end joining, free ends of DNA may be rejoined by an alternative pathway biased toward microhomology joins.^[6] With the exception of the μ and δ genes, only one antibody class is expressed by a B cell at any point in time.

Cytokines responsible for class switching[edit]

T cell cytokines are responsible for class switching in mouse (Table 1) and human (Table 2).^[7] ^[8] These cytokines may have suppressive effect on production of IgM.

Table 1. Class switching in mouse
T cells	Cytokines	Immunoglobulin classes
T cells	Cytokines	IgG1	IgG2a	IgG2b	IgG3	IgA	IgE
Th2	IL-4	↑	↓	↓	↓	↓	↑
Th2	IL-5					↑
Th1	IFNγ	↓	↑	↓	↓	↓	↓
Treg	TGFβ			↑	↓	↑

Table 2. Class switching in human
T cells	Cytokines	Immunoglobulin classes
T cells	Cytokines	IgG1	IgG2	IgG3	IgG4	IgA	IgE
Th2	IL-4				↑		↑
Th2	IL-5					↑
Th1	IFNγ	↑
Treg	TGFβ					↑

References[edit]

^ Eleonora Market, F. Nina Papavasiliou (2003) V(D)J Recombination and the Evolution of the Adaptive Immune System PLoS Biology1(1): e16.
^ Stavnezer J, Amemiya CT (2004). "Evolution of isotype switching". Semin. Immunol. 16 (4): 257–75. doi:10.1016/j.smim.2004.08.005. PMID 15522624.
^ Durandy A (2003). "Activation-induced cytidine deaminase: a dual role in class-switch recombination and somatic hypermutation". Eur. J. Immunol. 33 (8): 2069–73. doi:10.1002/eji.200324133. PMID 12884279.
^ Casali P, Zan H (2004). "Class switching and Myc translocation: how does DNA break?". Nat. Immunol. 5 (11): 1101–3. doi:10.1038/ni1104-1101. PMID 15496946.
^ Lieber MR, Yu K, Raghavan SC (2006). "Roles of nonhomologous DNA end joining, V(D)J recombination, and class switch recombination in chromosomal translocations". DNA Repair (Amst.) 5 (9-10): 1234–45. doi:10.1016/j.dnarep.2006.05.013. PMID 16793349.
^ Yan CT, Boboila C, Souza EK, Franco S, Hickernell TR, Murphy M, Gumaste S, Geyer M, Zarrin AA, Manis JP, Rajewsky K, Alt FW (2007). "IgH class switching and translocations use a robust non-classical end-joining pathway". Nature 449 (7161): 478–82. doi:10.1038/nature06020. PMID 17713479.
^ Janeway CA Jr., Travers P, Walport M, Shlomchik MJ (2001). Immunobiology. (5th ed.). Garland Publishing. (via NCBI Bookshelf) ISBN 0-8153-3642-X.
^ Male D, Brostoff J, Roth DB, Roitt I (2006). Immunology, 7th ed. Philadelphia: Mosby Elsevier, ISBN 978-0-323-03399-2 (pbk.)

External links[edit]

Immunoglobulin class switching at the US National Library of Medicine Medical Subject Headings (MeSH)
Diagram and description at med.sc.edu (see Figure 10)
Diagram at umassmed.edu
Diagram and description at cam.ac.uk
Diagram at utoronto.ca

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. 免疫遺伝学 immunoglobulin genetics
2. バーキットリンパ腫の病理学 pathobiology of burkitt lymphoma
3. 高IgM症候群 hyperimmunoglobulin m syndromes
4. 原発性の体液性免疫不全：概要 primary humoral immunodeficiencies an overview
5. 免疫グロブリンの構造 structure of immunoglobulins

English Journal

Positive Bioluminescence Imaging of MicroRNA Expression in Small Animal Models Using an Engineered Genetic-Switch Expression System, RILES.

Baril P1, Pichon C2.
Methods in molecular biology (Clifton, N.J.).Methods Mol Biol.2016;1372:193-208. doi: 10.1007/978-1-4939-3148-4_15.
MicroRNAs (miRNAs) are a class of small, noncoding RNAs which regulate gene expression by directing their target mRNA for degradation or translational repression. Since their discovery in the early 1990s, miRNAs have emerged as key components in the posttranscriptional regulation of gene networks, s
PMID 26530925

Responses in ileal and cecal bacteria to low and high amylose/amylopectin ratio diets in growing pigs.

Luo YH1, Yang C1, Wright AD2, He J1, Chen DW3.
Applied microbiology and biotechnology.Appl Microbiol Biotechnol.2015 Dec;99(24):10627-38. doi: 10.1007/s00253-015-6917-2. Epub 2015 Aug 30.
Dietary starch that escapes digestion in the small intestine may serve as a carbon source for bacterial fermentation in the distal intestine. This study aimed to compare the bacterial community in the ileal and cecal digesta of growing pigs fed diets with low (0.14, LR pigs) and high (0.43, HR pigs)
PMID 26318448

Japanese Journal

Inflammation-associated cancer development in digestive organs: mechanisms and roles for genetic and epigenetic modulation.

Chiba Tsutomu,Marusawa Hiroyuki,Ushijima Toshikazu
Gastroenterology 143(3), 550-563, 2012-09
… Among these, recent studies highlighted an important role of activation-induced cytidine deaminase, a nucleotide-editing enzyme essential for somatic hypermutation and class-switch recombination of the immunoglobulin gene, as a genomic modulator in inflammation-associated cancer development. …
NAID 120004873775

Related Pictures

★リンクテーブル★

リンク元	「クラス転換」
拡張検索	「immunoglobulin class switching」「class switching」「class switch recombination」
関連記事	「class」「switch」「switching」