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a class of proteins produced in lymph tissue in vertebrates and that function as antibodies in the immune response (同)Ig, immune serum globulin, immune gamma globulin, immune_globulin
the 7th letter of the Roman alphabet (同)g

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2013/06/18 12:03:46」(JST)

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Immunoglobulin G (IgG) is an antibody isotype. It is a protein complex composed of four peptide chains — two identical heavy chains and two identical light chains arranged in a Y-shape typical of antibody monomers. Each IgG has two antigen binding sites. Representing approximately 75% of serum immunoglobulins in humans, IgG is the most abundant antibody isotype found in the circulation.^[1] IgG molecules are synthesized and secreted by plasma B cells.

Functions[edit]

Antibodies are major components of the immune system. IgG is the main antibody isotype found in blood and extracellular fluid allowing it to control infection of body tissues. By binding many kinds of pathogens—representing viruses, bacteria, and fungi—IgG protects the body from infection. It does this via several immune mechanisms: IgG-mediated binding of pathogens causes their immobilization and binding together via agglutination; IgG coating of pathogen surfaces (known as opsonization) allows their recognition and ingestion by phagocytic immune cells; IgG activates the classical pathway of the complement system, a cascade of immune protein production that results in pathogen elimination; IgG also binds and neutralizes toxins. IgG also plays an important role in antibody-dependent cell-mediated cytotoxicity (ADCC) and intracellular antibody-mediated proteolysis, in which it binds to TRIM21 (the receptor with greatest affinity to IgG in humans) in order to direct marked virions to the proteasome in the cytosol.^[2] IgG is also associated with Type II and Type III Hypersensitivity. IgG antibodies are generated following class switching and maturation of the antibody response and thus participate predominantly in the secondary immune response.^[3] IgG is secreted as a monomer that is small in size allowing it to easily perfuse tissues. It is the only isotype that can pass through the human placenta, thereby providing protection to the fetus in utero. Along with IgA secreted in the breast milk, residual IgG absorbed through the placenta provides the neonate with humoral immunity before its own immune system develops. Colostrum contains a high percentage of IgG, especially bovine colostrum. In individuals with prior immunity to a pathogen, IgG appears about 24–48 hours after antigenic stimulation.

Structure[edit]

Immunoglobulin

IgG antibodies are large molecules of about 150 kDa composed of four peptide chains. It contains two identical class γ heavy chains of about 50 kDa and two identical light chains of about 25 kDa, thus a tetrameric quaternary structure. The two heavy chains are linked to each other and to a light chain each by disulfide bonds. The resulting tetramer has two identical halves, which together form the Y-like shape. Each end of the fork contains an identical antigen binding site. The Fc regions of IgGs bear a highly conserved N-glycosylation site. The N-glycans attached to this site are predominantly core-fucosylated diantennary structures of the complex type. In addition, small amounts of these N-glycans also bear bisecting GlcNAc and α-2,6-linked sialic acid residues.^[4]

Subclasses[edit]

There are four IgG subclasses (IgG1, 2, 3, and 4) in humans, named in order of their abundance in serum (IgG1 being the most abundant).

Name	Percent	Crosses placenta easily	Complement activator	Binds to Fc receptor on phagocytic cells
IgG1	66%	yes (1.47)†	second-highest	high affinity
IgG2	23%	no (0.8)†	third-highest	extremely low affinity
IgG3	7%	yes (1.17)†	highest	high affinity
IgG4	4%	yes (1.15)†	no	intermediate affinity
†: Quota cord/maternity concentrations blood. Based on data from a Japanese study on 228 mothers. ^[5]

Note: IgG affinity to Fc receptors on phagocytic cells is specific to individual species from which the antibody comes as well as the class. The structure of the hinge regions (region 6 in the diagram) gives each of the four IgG classes its unique biological profile. Even though there is about 95% similarity between their Fc regions, the structure of the hinge regions is relatively different.

The relative ability of different IgG subclasses to fix complement may explain why some anti-donor antibody responses do not harm a graft after organ transplantation.^[6]

In a model of autoantibody mediated anemia using IgG isotype switch variants of an anti erythrocytes autoantibody, it was found that IgG2a was superior to IgG1 in activating complement. Moreover, it was found that the IgG2a isotype was able to interact very efficiently with FcgammaR. As a result, 20 times higher doses of IgG1, in relationship to IgG2a autoantibodies, were required to induce autoantibody mediated pathology. ^[7]

Use as diagnostic[edit]

The measurement of immunoglobulin G can be a diagnostic tool for certain conditions if indicated by certain symptoms. ^[8]^{[citation needed]} Clinically, measured IgG antibody levels are generally considered to be indicative of an individual's immune status to particular pathogens. A common example of this practice are titers drawn to demonstrate serologic immunity to measles, mumps, and rubella (MMR), hepatitis B virus, and varicella (chickenpox), among others.^[9]

Testing of IgG is not indicated for diagnosis of allergy.^[10]^[11]

References[edit]

^ Junqueira, Luiz C.; Jose Carneiro (2003). Basic Histology. McGraw-Hill. ISBN 0-8385-0590-2.
^ Mallery DL, McEwan WA, Bidgood SR, Towers GJ, Johnson CM, James LC (2010). "Antibodies mediate intracellular immunity through tripartite motif-containing 21 (TRIM21)". Proc. Natl. Acad. Sci. U.S.A. 107 (46): 19985–19990. doi:10.1073/pnas.1014074107. PMC 2993423. PMID 21045130.
^ Meulenbroek, A.J.; Zeijlemaker, W.P. (1996).
^ Stadlmann J, Pabst M, Kolarich D, Kunert R, Altmann F. (2008). "Analysis of immunoglobulin glycosylation by LC-ESI-MS of glycopeptides and oligosaccharides". Proteomics 8 (14): 2858–2871. doi:10.1002/pmic.200700968. PMID 18655055.
^ Hashira S, Okitsu-Negishi S, Yoshino K (August 2000). "Placental transfer of IgG subclasses in a Japanese population". Pediatr Int 42 (4): 337–42. doi:10.1046/j.1442-200x.2000.01245.x. PMID 10986861.
^ ZH Gao et al.; McAlister, VC; Wright Jr, JR; McAlister, CC; Peltekian, K; MacDonald, AS (2004). "Immunoglobulin-G subclass antidonor reactivity in transplant recipients". Liver Transplantation 10 (8): 1055–1059. doi:10.1002/lt.20154. PMID 15390333.
^ Azeredo et al. J of Exp Med. 2002. 195: 665.
^ [G] (2008 Mar-Apr). Anti-cyclic citrullinated peptide antibodies of IgG isotype are specific diagnostic markers of rheumatoid arthritis. Clinical and Experimental Rheumatology
^ "For physicians and hospitals". Quest Diagnostics.
^ American Academy of Allergy, Asthma, and Immunology. "Five Things Physicians and Patients Should Question". Choosing Wisely: an initiative of the ABIM Foundation (American Academy of Allergy, Asthma, and Immunology). Retrieved August 14, 2012
^ Cox, L.; Williams, B.; Sicherer, S.; Oppenheimer, J.; Sher, L.; Hamilton, R.; Golden, D.; American College Of Allergy, A. I. T. T. F. et al. (2008). "Pearls and pitfalls of allergy diagnostic testing: Report from the American College of Allergy, Asthma and Immunology/American Academy of Allergy, Asthma and Immunology Specific IgE Test Task Force". Annals of allergy, asthma & immunology : official publication of the American College of Allergy, Asthma, & Immunology 101 (6): 580–592. doi:10.1016/S1081-1206(10)60220-7. PMID 19119701. |displayauthors= suggested (help) edit

External links[edit]

Janeway Immunobiology - The structure of a typical antibody (IgG)
A booklet with everything you wanted to know about IgG subclasses

UpToDate Contents

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1. IgGサブクラス：物理学的性質、遺伝的特徴、および生物学的機能 igg subclasses physical properties genetics and biologic functions
2. IgG サブクラス欠乏症 igg subclass deficiency
3. IgG4関連疾患の概要 overview of igg4 related disease
4. 幼児期の一過性低ガンマグロブリン血症 transient hypogammaglobulinemia of infancy
5. 免疫グロブリンの構造 structure of immunoglobulins

English Journal

Specific IgG and IgA of common foods in Chinese children with eczema: friend or foe.

Hon KL1, Poon TC, Pong NH, Wong YH, Leung SS, Chow CM, Leung TF.
The Journal of dermatological treatment.J Dermatolog Treat.2014 Dec;25(6):462-6. doi: 10.3109/09546634.2013.848262. Epub 2013 Nov 15.
BACKGROUND: Specific immunoglobulins G and A (IgG and IgA) for common food items have been extensively measured as surrogate markers of food allergy, and dietary avoidance based on the test results advocated.AIM: We reviewed the prevalence of specific food IgG and IgA in children with eczema and eva
PMID 24237254

Cardiometabolic biomarkers in chronic plaque psoriasis before and after etanercept treatment.

Puig L1, Strohal R, Fuiman J, Pedersen R, Szumski A, Koenig AS, Robertson D, Drexel H.
The Journal of dermatological treatment.J Dermatolog Treat.2014 Dec;25(6):470-81. doi: 10.3109/09546634.2013.848260. Epub 2013 Nov 13.
OBJECTIVE: To assess cardiometabolic biomarkers in patients with psoriasis before and after etanercept treatment.METHODS: Patients with moderate-to-severe plaque psoriasis were randomized to etanercept 50 mg once or twice weekly, double-blinded. Cardiometabolic biomarkers were assessed at baseline
PMID 24219012

Towards sensitive label-free immunosensing by means of turn-around point long period fiber gratings.

Chiavaioli F1, Biswas P2, Trono C3, Bandyopadhyay S4, Giannetti A1, Tombelli S1, Basumallick N4, Dasgupta K4, Baldini F1.
Biosensors & bioelectronics.Biosens Bioelectron.2014 Oct 15;60:305-10. doi: 10.1016/j.bios.2014.04.042. Epub 2014 May 2.
Long period fiber gratings have been effectively used in the field of biochemical sensing since a few years. Compared to other well-known label-free optical approaches, long period gratings (LPGs) take advantage of the typical peculiarity of optical fibers. Coupling the propagating core mode with a
PMID 24835405

Japanese Journal

Adhesion of Enterohemorrhagic Escherichia coli O157:H7 to the Intestinal Epithelia Is Essential for Inducing Secretory IgA Antibody Production in the Intestine of Mice

Nagano Keiji,Taguchi Kazuki,Tokoro Shunji,Tatsuno Ichiro,Mori Hiroshi
Biological and Pharmaceutical Bulletin 37(3), 409-416, 2014
… We examined whether adherence of enterohemorrhagic Escherichia coli (EHEC) O157:H7 to intestinal epithelial cells contributed to the induction of secretory immunoglobulin A (IgA) antibody production in mice. … Kanamycin (Km)-treated mice showed prolonged and similar fecal shedding of Km-resistant mutants of EHEC O157:H7 including A2-F6 having intact LEE, A6-E7 (sepL-insertion mutant), G1-E11 (tir-insertion mutant) and Δeae (eae-deletion mutant). …
NAID 130003390946

Serum galectin-9 levels are elevated in the patients with type 2 diabetes and chronic kidney disease

Kurose Yuko,Wada Jun,Kanzaki Motoko,Teshigawara Sanae,Nakatsuka Atsuko,Murakami Kazutoshi,Inoue Kentaro,Terami Takahiro,Katayama Akihiro,Watanabe Mayu,Higuchi Chigusa,Eguchi Jun,Miyatake Nobuyuki,Makino Hirofumi
BMC Nephrology 14, 2013-01-22
… Background: Galectin-9 (Gal-9) induces apoptosis in activated T helper 1 (T(H)1) cells as a ligand for T cell immunoglobulin mucin-3 (Tim-3). … Gal-9 also inhibits the G1 phase cell cycle arrest and hypertrophy in db/db mice, the hallmark of early diabetic nephropathy, by reversing the high glucose-induced up-regulation of cyclin dependent kinase inhibitors such as p27(Kip1) and p21(Cip1). …
NAID 120005324795

Vaccination with Plasmid DNA Encoding a Mutant Toxic Shock Syndrome Toxin-1 Ameliorates Toxin-induced Lethal Shock in Mice

Feng Mao-Hui,Cui Jing-Chun,Nakane Akio,Hu Dong-Liang
The Tohoku Journal of Experimental Medicine 231(1), 1-8, 2013
… Immunization with pcDNA-mTSST-1 plus mLT increased the serum levels of TSST-1-specific antibodies, especially immunoglobulin G1 (IgG1) and IgG2a subclasses. …
NAID 130004460083

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