Antibodies

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An antibody, otherwise known as an [[Immunoglobulin|immunoglobin]], is a Y-shaped [[Protein|protein]] produced by the body's [[Immune system|immune system]] when foreign objects are detected. Antibodies are secreted by [[B-cells|B cells]] during an immune response and comprises the majority of the humoral immune response. The antibody recognises a specific site on the foreign target called [[Antigens|antigens]].  
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An antibody, otherwise known as an [[Immunoglobulin|immunoglobin]], is a Y-shaped [[Protein|protein]] produced by the body's [[Immune system|immune system]] when foreign objects are detected. Antibodies are secreted by [[B-cells|B cells]] during an immune response and comprise the majority of the humoral immune response. Ab cell secretes vast array antibodies that are similar in structure but not identical<ref>Klaus DE. Immunology: Understanding the immune system. 2nd edition. John Wiley and Sons Ltd. 2009</ref>.The antibody recognises a specific site on the foreign target called [[Antigens|antigens]].  
  
The antibody then binds to the [[Antigens|antigens]] in order to remove them from the body.&nbsp;<span style="line-height: 1.5em">A wide range of substances are regarded as [[Antigens|antigens]], such as toxic materials like insect venom<ref>The Editors of Encyclopaedia Britannica (2014) Antibody http://www.britannica.com/EBchecked/topic/27783/antibody (last accessed 19/11/14)</ref>.</span>
+
The antibody then binds to the [[Antigens|antigens]] in order to remove them from the body. A wide range of substances are regarded as [[Antigens|antigens]], such as toxic materials like insect venom<ref>The Editors of Encyclopaedia Britannica (2014) Antibody http://www.britannica.com/EBchecked/topic/27783/antibody (last accessed 19/11/14)</ref>.  
  
However, antibodies can also be produced when healthy [[Tissue|tissue]] is mistaken for a harmful substance by the [[Immune system|immune system]]. This is known as an [[Autoimmune disease|autoimmune disorder]]<ref>David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by A.D.A.M. Health Solutions, Ebix, Inc., Editorial Team: David Zieve, MD, MHA, David R. Eltz, and Stephanie Slon. (2012) Antibody.http://www.nlm.nih.gov/medlineplus/ency/article/002223.htm (last accessed 19/11/14)</ref>.<br>
+
However, antibodies can also be produced when healthy [[Tissue|tissue]] is mistaken for a harmful substance by the [[Immune system|immune system]]. This is known as an [[Autoimmune disease|autoimmune disorder]]<ref>David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by A.D.A.M. Health Solutions, Ebix, Inc., Editorial Team: David Zieve, MD, MHA, David R. Eltz, and Stephanie Slon. (2012) Antibody.http://www.nlm.nih.gov/medlineplus/ency/article/002223.htm (last accessed 19/11/14)</ref>.  
  
 
Antibody-antigen interactions can also explain other biological processes such as the [[Blood group systems|ABO blood group system]]<ref>Weir, D. and Spencer, J. (1997) Immunology, 8th edition, page 7 New York: Churchill Livingstone</ref>.  
 
Antibody-antigen interactions can also explain other biological processes such as the [[Blood group systems|ABO blood group system]]<ref>Weir, D. and Spencer, J. (1997) Immunology, 8th edition, page 7 New York: Churchill Livingstone</ref>.  
  
=== Structure of Antibodies'''&nbsp;''' ===
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=== Structure of Antibodies  ===
  
Antibodies are composed of subunits of [[Amino acids|amino acids]]. The basis of the bivalent antibody molecule are four [[Polypeptide chain|polypeptide chains]], within which are distinguished into two types, referred to as light (classed as either lambda or kappa) and heavy chain. The light chain is around 25 kDa, and the heavy chain is 50 kDa. There are five classes of antibodies, and therefore the heavy chain is important for determining which class the immunoglobulin belongs to&nbsp;[[Image:Antibody.gif|left|Structure of an Antibody]].
+
Antibodies are composed of subunits of [[Amino acids|amino acids]]. The basis of the bivalent antibody molecule are four [[Polypeptide chain|polypeptide chains]], within which are distinguished into two types, referred to as light (classed as either lambda or kappa) and heavy chain. The light chain is around 25 kDa, and the heavy chain is 50 kDa. There are five classes of antibodies, and therefore the heavy chain is important for determining which class the immunoglobulin belongs to [[Image:Antibody.gif|left|Structure of an Antibody]].  
  
It is these heavy chains which enable antibodies to be separated into the five classes (or&nbsp;isotypes)&nbsp;of immunoglobins; IgG, IgA, IgD, IgM and IgE. The way in which the two heavy chains are connected to one another is through disulphide bonds, they are then connected to a light chain by [[Disulphide bond|disulphide bonds]] as well. This, therefore, creates two identical antigen-binding sites<ref>Janeway CA, Shlomchik MJ, Travers P, and nbsp;Walport M. Immunobiology: The Immune System in Health and Disease: 5th ed. New York, NY: Garland Science; 2001.</ref>.<br>
+
It is these heavy chains which enable antibodies to be separated into the five classes (or isotypes) of immunoglobins; IgG, IgA, IgD, IgM and IgE. The way in which the two heavy chains are connected to one another is through disulphide bonds, they are then connected to a light chain by [[Disulphide bond|disulphide bonds]] as well. This, therefore, creates two identical antigen-binding sites<ref>Janeway CA, Shlomchik MJ, Travers P, and Walport M. Immunobiology: The Immune System in Health and Disease: 5th ed. New York, NY: Garland Science; 2001.</ref>.  
  
The regions of the heavy chain includes three constant domains, which are the same for all antibodies, and the one variable domain. The light chains are also composed of a constant domain and a variable domain. The variable regions of the antibodies are where the [[Antigen|antigen]] binding site is located and the constant domain is responsible for the outcome of the antigen<ref>Fanger M, Lydyard P, Whelan A. Immunology: 3rd ed. New York, NY: Garland Science; 2011.</ref>. The Fc region is the part of the antibody that binds to cell surface receptors on cells such as [[Macrophage|macrophages]]. Finally, the Fab region is primarily known as the location for the antigen binding site<ref>Novimmune. Antibodies [Internet]. Geneva, Switzerland; Novimmune SA; 2015 [cited 2015 Nov 20]. Available from: http://www.novimmune.com/science/antibodies.html</ref>. The domains of antibodies are around 110 amino acids in length.  
+
The regions of the heavy chain include three constant domains, which are the same for all antibodies, and the one variable domain. The light chains are also composed of a constant domain and a variable domain. The variable regions of the antibodies are where the [[Antigen|antigen]] binding site is located and the constant domain is responsible for the outcome of the antigen<ref>Fanger M, Lydyard P, Whelan A. Immunology: 3rd ed. New York, NY: Garland Science; 2011.</ref>. The Fc region is the part of the antibody that binds to cell surface receptors on cells such as [[Macrophage|macrophages]]. Finally, the Fab region is primarily known as the location for the antigen binding site<ref>Novimmune. Antibodies [Internet]. Geneva, Switzerland; Novimmune SA; 2015 [cited 2015 Nov 20]. Available from: http://www.novimmune.com/science/antibodies.html</ref>. The domains of antibodies are around 110 amino acids in length.  
  
The five classes of immunoglobulins have different functions in order to protect the body. IgA is present on the membrane of mucosal epithelial cells and is then released in fluids such as saliva and tears. This immunoglobulin protects the mucosal surfaces by, for example, binding to microorganisms to prevent them from attaching to the mucosal surfaces. IgG is the main antibody and has many roles including the promotion of [[Phagocytosis|phagocytosis]] of invading pathogens. IgM is especially effective at binding to antigens on pathogens and causing agglutination to prevent them from infecting other body cells. Immunoglobulin M is present on the membrane of [[B-cells|B-cells]]. IgE are involved in causing inflammation when an allergen enters the body (allergic reaction) and does this by stimulating mast cells which leads to the release of mediators. Finally, IgD is also present on B-cells and is thought to work with IgM<ref>Arthur Rabson AR. Ivan M.Roitt IM. Peter J.Delves PJ. Really Essential Medical Immunology. 2nd Edition. Oxford: Blackwell Publishing Ltd. 2005.</ref><sup>.</sup>
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The five classes of immunoglobulins have different functions in order to protect the body. IgA is present on the membrane of mucosal epithelial cells and is then released in fluids such as saliva and tears. This immunoglobulin protects the mucosal surfaces by, for example, binding to microorganisms to prevent them from attaching to the mucosal surfaces. IgG is the main antibody making up around 80% of all antibodies found in the plasma and has many roles including the promotion of [[Phagocytosis|phagocytosis]] of invading pathogens. IgM is especially effective at binding to antigens on pathogens and causing agglutination to prevent them from infecting other body cells. Immunoglobulin M is present on the membrane of [[B-cells|B-cells]]. IgE are involved in causing inflammation when an allergen enters the body (allergic reaction) and does this by stimulating mast cells which leads to the release of mediators. Finally, IgD is also present on B-cells and is thought to work with IgM<ref>Arthur Rabson AR. Ivan M.Roitt IM. Peter J.Delves PJ. Really Essential Medical Immunology. 2nd Edition. Oxford: Blackwell Publishing Ltd. 2005.</ref>.  
  
 
=== Antigen-antibody interactions  ===
 
=== Antigen-antibody interactions  ===
  
The antigen-antibody interactions are formed by a combination of bonds, such as [[Hydrogen bond|hydrogen]], [[Van der waals forces|van der Waals]] and electrostatic forces. [[Affinity|Affinity]] is used to measure the strength of the interaction between an [[Epitopes|epitope]] and the antigen-binding site. It can be defined by the [[Affinity|affinity constant ]]K<sub>A, </sub>whereby it describes the extent of how much of the antigen-antibody complex exist when [[Equilibrium|equilibrium]] is reached. The time it takes depends on factors such as [[Diffusion|diffusion]] rate. Therefore, high-affinity antibodies will bind a larger amount of antibodies, in contrast to low-affinity antibodies. As a result, the affinity of monoclonal antibodies is measured more accurately (compared to polyclonal antibodies as they are selective for only one epitope. Avidity measures the overall strength of 3 factors: affinity of the antibody to epitope, antibody and antigen valency and the interactions of the structural arrangements. As antibodies are multivalent, the interactions help enhance their stability as high avidity structures are being formed<ref name="null">Bio-Rad. Avidity and affinity of antibodies. 2016. Available from: https://www.bio-rad-antibodies.com/antigen-antibody-interactions.html (Last accessed 18/10/16)</ref>.  
+
The antigen-antibody interactions are formed by a combination of bonds, such as [[Hydrogen bond|hydrogen]], London Dispersion Forces&nbsp;and electrostatic forces. [[Affinity|Affinity]] is used to measure the strength of the interaction between an [[Epitopes|epitope]] and the antigen-binding site. It can be defined by the [[Affinity|affinity constant ]]K<sub>A, </sub>whereby it describes the extent of how much of the antigen-antibody complex exist when [[Equilibrium|equilibrium]] is reached. The time it takes depends on factors such as [[Diffusion|diffusion]] rate. Therefore, high-affinity antibodies will bind a larger amount of antibodies, in contrast to low-affinity antibodies. As a result, the affinity of monoclonal antibodies is measured more accurately (compared to polyclonal antibodies as they are selective for only one epitope. Avidity measures the overall strength of 3 factors: affinity of the antibody to epitope, antibody and antigen valency and the interactions of the structural arrangements. As antibodies are multivalent, the interactions help enhance their stability as high avidity structures are being formed<ref name="null">Bio-Rad. Avidity and affinity of antibodies. 2016. Available from: https://www.bio-rad-antibodies.com/antigen-antibody-interactions.html (Last accessed 18/10/16)</ref>.  
  
 
=== Origin of Antibodies  ===
 
=== Origin of Antibodies  ===
  
Antibodies are produced by plasma cells which have originated from [[B lymphocytes|B lymphocytes]].&nbsp;<br>
+
Antibodies are produced by plasma cells which have originated from [[B lymphocytes|B lymphocytes]].  
  
There is a complementary antibody to every antigen because of the variability in the structure of the different classes and subclasses of antibodies<ref>Structure of an Antibody image. Available on: http://www.biology.arizona.edu/immunology/tutorials/antibody/structure.html</ref>.&nbsp;
+
There is a complementary antibody to every antigen because of the variability in the structure of the different classes and subclasses of antibodies<ref>Structure of an Antibody image. Available on: http://www.biology.arizona.edu/immunology/tutorials/antibody/structure.html</ref>.  
  
 
=== References  ===
 
=== References  ===
  
 
<references />
 
<references />

Latest revision as of 17:41, 9 December 2018

An antibody, otherwise known as an immunoglobin, is a Y-shaped protein produced by the body's immune system when foreign objects are detected. Antibodies are secreted by B cells during an immune response and comprise the majority of the humoral immune response. Ab cell secretes vast array antibodies that are similar in structure but not identical[1].The antibody recognises a specific site on the foreign target called antigens.

The antibody then binds to the antigens in order to remove them from the body. A wide range of substances are regarded as antigens, such as toxic materials like insect venom[2].

However, antibodies can also be produced when healthy tissue is mistaken for a harmful substance by the immune system. This is known as an autoimmune disorder[3].

Antibody-antigen interactions can also explain other biological processes such as the ABO blood group system[4].

Contents

Structure of Antibodies

Antibodies are composed of subunits of amino acids. The basis of the bivalent antibody molecule are four polypeptide chains, within which are distinguished into two types, referred to as light (classed as either lambda or kappa) and heavy chain. The light chain is around 25 kDa, and the heavy chain is 50 kDa. There are five classes of antibodies, and therefore the heavy chain is important for determining which class the immunoglobulin belongs to
Structure of an Antibody
.

It is these heavy chains which enable antibodies to be separated into the five classes (or isotypes) of immunoglobins; IgG, IgA, IgD, IgM and IgE. The way in which the two heavy chains are connected to one another is through disulphide bonds, they are then connected to a light chain by disulphide bonds as well. This, therefore, creates two identical antigen-binding sites[5].

The regions of the heavy chain include three constant domains, which are the same for all antibodies, and the one variable domain. The light chains are also composed of a constant domain and a variable domain. The variable regions of the antibodies are where the antigen binding site is located and the constant domain is responsible for the outcome of the antigen[6]. The Fc region is the part of the antibody that binds to cell surface receptors on cells such as macrophages. Finally, the Fab region is primarily known as the location for the antigen binding site[7]. The domains of antibodies are around 110 amino acids in length.

The five classes of immunoglobulins have different functions in order to protect the body. IgA is present on the membrane of mucosal epithelial cells and is then released in fluids such as saliva and tears. This immunoglobulin protects the mucosal surfaces by, for example, binding to microorganisms to prevent them from attaching to the mucosal surfaces. IgG is the main antibody making up around 80% of all antibodies found in the plasma and has many roles including the promotion of phagocytosis of invading pathogens. IgM is especially effective at binding to antigens on pathogens and causing agglutination to prevent them from infecting other body cells. Immunoglobulin M is present on the membrane of B-cells. IgE are involved in causing inflammation when an allergen enters the body (allergic reaction) and does this by stimulating mast cells which leads to the release of mediators. Finally, IgD is also present on B-cells and is thought to work with IgM[8].

Antigen-antibody interactions

The antigen-antibody interactions are formed by a combination of bonds, such as hydrogen, London Dispersion Forces and electrostatic forces. Affinity is used to measure the strength of the interaction between an epitope and the antigen-binding site. It can be defined by the affinity constant KA, whereby it describes the extent of how much of the antigen-antibody complex exist when equilibrium is reached. The time it takes depends on factors such as diffusion rate. Therefore, high-affinity antibodies will bind a larger amount of antibodies, in contrast to low-affinity antibodies. As a result, the affinity of monoclonal antibodies is measured more accurately (compared to polyclonal antibodies as they are selective for only one epitope. Avidity measures the overall strength of 3 factors: affinity of the antibody to epitope, antibody and antigen valency and the interactions of the structural arrangements. As antibodies are multivalent, the interactions help enhance their stability as high avidity structures are being formed[9].

Origin of Antibodies

Antibodies are produced by plasma cells which have originated from B lymphocytes.

There is a complementary antibody to every antigen because of the variability in the structure of the different classes and subclasses of antibodies[10].

References

  1. Klaus DE. Immunology: Understanding the immune system. 2nd edition. John Wiley and Sons Ltd. 2009
  2. The Editors of Encyclopaedia Britannica (2014) Antibody http://www.britannica.com/EBchecked/topic/27783/antibody (last accessed 19/11/14)
  3. David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by A.D.A.M. Health Solutions, Ebix, Inc., Editorial Team: David Zieve, MD, MHA, David R. Eltz, and Stephanie Slon. (2012) Antibody.http://www.nlm.nih.gov/medlineplus/ency/article/002223.htm (last accessed 19/11/14)
  4. Weir, D. and Spencer, J. (1997) Immunology, 8th edition, page 7 New York: Churchill Livingstone
  5. Janeway CA, Shlomchik MJ, Travers P, and Walport M. Immunobiology: The Immune System in Health and Disease: 5th ed. New York, NY: Garland Science; 2001.
  6. Fanger M, Lydyard P, Whelan A. Immunology: 3rd ed. New York, NY: Garland Science; 2011.
  7. Novimmune. Antibodies [Internet]. Geneva, Switzerland; Novimmune SA; 2015 [cited 2015 Nov 20]. Available from: http://www.novimmune.com/science/antibodies.html
  8. Arthur Rabson AR. Ivan M.Roitt IM. Peter J.Delves PJ. Really Essential Medical Immunology. 2nd Edition. Oxford: Blackwell Publishing Ltd. 2005.
  9. Bio-Rad. Avidity and affinity of antibodies. 2016. Available from: https://www.bio-rad-antibodies.com/antigen-antibody-interactions.html (Last accessed 18/10/16)
  10. Structure of an Antibody image. Available on: http://www.biology.arizona.edu/immunology/tutorials/antibody/structure.html
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