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[[Immunoglobulin|Immunoglobulin]] G (IgG) is an [[Antibody|antibody]], which is abundant in the [[Blood|blood]], | [[Immunoglobulin|Immunoglobulin]] G (IgG) is an [[Antibody|antibody]], which is abundant in the [[Blood|blood]], lymph and extracellular fluid <ref>Parham,P. (2009) The Imuune System, 3rd edition, New York, Garland Science</ref>. | ||
IgG plays various roles in the [[Immune response|immune response]], but primarily , it aids the phagocytosis of [[Pathogen|pathogens]] and alleviates their destruction <ref>Parham, P. (2009)The Immune System, 3rd edition, New York, Garland Science</ref>. IgG acts by coating the [[Microorganism|microorganism]], a process known as 'opsonization' and then binds to [[Phagocytes|phagocytes]] through its constant regions (Fc receptors). Being coated by the IgG, the pathogen is captured by the [[Neutrophil|neutrophils]] and the [[Macrophage|macrophages]] and finally undergoes destruction by the latter <ref>Parham, P. (2009)The Immune System, 3rd edition, New York, Garland Science</ref>. | IgG plays various roles in the [[Immune response|immune response]], but primarily, it aids the phagocytosis of [[Pathogen|pathogens]] and alleviates their destruction <ref>Parham, P. (2009)The Immune System, 3rd edition, New York, Garland Science</ref>. IgG acts by coating the [[Microorganism|microorganism]], a process known as 'opsonization' (UK spelling: opsonisation) and then binds to [[Phagocytes|phagocytes]] through its constant regions (Fc receptors). Being coated by the IgG, the pathogen is captured by the [[Neutrophil|neutrophils]] and the [[Macrophage|macrophages]] and finally undergoes destruction by the latter <ref>Parham, P. (2009)The Immune System, 3rd edition, New York, Garland Science</ref>. | ||
During pregnancy, IgG are the only type of human [[Antibody|antibodies]] that can | During pregnancy, IgG are the only type of human [[Antibody|antibodies]] that can pass from mother to the foetus. Cells at the placenta have Fc receptors that bind to the IgG antibodies in the mother’s blood. Consequently, IgG is [[Endocytosis|endocytosed]] in the form of a vesicle across the cell and expelled into the fetus’ blood<ref>Janeway CA Jr, Travers P, Walport M, et al (2001) Immunobiology: The Immune System in Health and Disease, 5th edition, New York: Garland Science; 2001.</ref>. | ||
== Structure == | == Structure == | ||
IgG has a molecular weight about 150kDa. It is composed of two light chains and two heavy gamma chains, each gamma chain having 4 domains. There are 4 subclasses of IgG; IgG1 (γ1 heavy chains), IgG2( γ2 heavy chains), IgG3 (γ3 heavy chains) and IgG4 (γ4 heavy chains). Furthermore [[ | IgG has a molecular weight about 150kDa. It is composed of two light chains and two heavy gamma chains, each gamma chain having 4 domains. There are 4 subclasses of IgG; IgG1 (γ1 heavy chains), IgG2( γ2 heavy chains), IgG3 (γ3 heavy chains) and IgG4 (γ4 heavy chains). Furthermore [[Isotype|isotypes]] exist with the light chains either being kappa κ or lambda λ<ref>Alberts B, et al (2008) Molecular Biology of the Cell, 5th edition, New York: Garland Science; p1554-5</ref>. These subclasses give rise to variations in properties and abundance of each type. | ||
At the end the [[N terminus|N terminus]] of each chain there is a variable region, known as the [[ | At the end the [[N terminus|N terminus]] of each chain there is a variable region, known as the [[Fragment antigen binding site|fragment antigen binding site]] Fab. Three [[Hypervariable loops|hypervariable loops]] from each chain are the determining region and are highly specific to the complimentary [[Antigen|antigen]]. Altogether six hypervariable regions (3 from the light chain and 3 from the heavy chain) form a Fab and each IgG antibody has 2 fragment antigen binding sites. The constant region, known as the Fragment Crystallisable Fc, interacts with receptors on cells during secondary immune responses and binds to C1q in the [[Classical Complement Pathway|Classical Complement Pathway]].<br>The IgG antibody chains are configured to produce a Y-shaped unit. The two heavy chains are joined by a hinge region, an intra-chain disulphide bond that allows the flexibility and movement of the Fab domains. The light variable chain and the heavy variable chain are also joined by an intra-chain [[Disulphide bond|disulphide bond]]<ref>Janeway CA Jr, Travers P, Walport M, et al (2001) Immunobiology: The Immune System in Health and Disease, 5th edition, New York: Garland Science; 2001.</ref>.<br> | ||
=== References: === | === References: === | ||
<references /> | <references /> | ||
Latest revision as of 13:45, 19 October 2015
Immunoglobulin G (IgG) is an antibody, which is abundant in the blood, lymph and extracellular fluid [1].
IgG plays various roles in the immune response, but primarily, it aids the phagocytosis of pathogens and alleviates their destruction [2]. IgG acts by coating the microorganism, a process known as 'opsonization' (UK spelling: opsonisation) and then binds to phagocytes through its constant regions (Fc receptors). Being coated by the IgG, the pathogen is captured by the neutrophils and the macrophages and finally undergoes destruction by the latter [3].
During pregnancy, IgG are the only type of human antibodies that can pass from mother to the foetus. Cells at the placenta have Fc receptors that bind to the IgG antibodies in the mother’s blood. Consequently, IgG is endocytosed in the form of a vesicle across the cell and expelled into the fetus’ blood[4].
Structure
IgG has a molecular weight about 150kDa. It is composed of two light chains and two heavy gamma chains, each gamma chain having 4 domains. There are 4 subclasses of IgG; IgG1 (γ1 heavy chains), IgG2( γ2 heavy chains), IgG3 (γ3 heavy chains) and IgG4 (γ4 heavy chains). Furthermore isotypes exist with the light chains either being kappa κ or lambda λ[5]. These subclasses give rise to variations in properties and abundance of each type.
At the end the N terminus of each chain there is a variable region, known as the fragment antigen binding site Fab. Three hypervariable loops from each chain are the determining region and are highly specific to the complimentary antigen. Altogether six hypervariable regions (3 from the light chain and 3 from the heavy chain) form a Fab and each IgG antibody has 2 fragment antigen binding sites. The constant region, known as the Fragment Crystallisable Fc, interacts with receptors on cells during secondary immune responses and binds to C1q in the Classical Complement Pathway.
The IgG antibody chains are configured to produce a Y-shaped unit. The two heavy chains are joined by a hinge region, an intra-chain disulphide bond that allows the flexibility and movement of the Fab domains. The light variable chain and the heavy variable chain are also joined by an intra-chain disulphide bond[6].
References:
- ↑ Parham,P. (2009) The Imuune System, 3rd edition, New York, Garland Science
- ↑ Parham, P. (2009)The Immune System, 3rd edition, New York, Garland Science
- ↑ Parham, P. (2009)The Immune System, 3rd edition, New York, Garland Science
- ↑ Janeway CA Jr, Travers P, Walport M, et al (2001) Immunobiology: The Immune System in Health and Disease, 5th edition, New York: Garland Science; 2001.
- ↑ Alberts B, et al (2008) Molecular Biology of the Cell, 5th edition, New York: Garland Science; p1554-5
- ↑ Janeway CA Jr, Travers P, Walport M, et al (2001) Immunobiology: The Immune System in Health and Disease, 5th edition, New York: Garland Science; 2001.