Antibody structure and function

• antibody structure and function

  • produced by B cell , form the B cell antigen specific receptor
  • soluble proteins found in blood and secretory fluids such as mucous + milk that bind specifically to foreign material antibodies.
  • Antibodies are known collectively as immunoglobulin (Ig)
  • Once bounds to antigens B cells will differentiate to produce plasma cells which. Make antibodies
• features of antibody

  • bi-functional - specificity + biological activory
  • the variable region binds the antigenic structure
  • biological activity is restricted to the constant region of the heavy chain
• Antibody structure

  
• antibody domain structure 


  composed of two chains- light and heavy which are made up of a variable and constant region

  the variation between antibodies is restricted to 3 regions within the N terminal domain of both the heavy and light chains.
• antibody domain functions 


  variable region - binds antigen

  constant region- biological function

  • opsoniation
  • activate complement
  • FcR mediated activity
• Hyper variable domain 


  • contact point for antigen
• generation of diversity of the variable light (K) chain

  • there are 40 variable and 5 joining gene segments
  • only one V and one J make a whole variable domain
  • therefore recombined diversity
  • two types of light chain
  • -kappa or - lambda
  • one immunoglobulin has either kpapa or lambda not both
• antibody affinity 


  • - measure the strength of a single antibody- antigen interaction - single fab with ag epitope - also known as the specific region.
• antibody avidity 


  • a measure of the interaction of an antibody with an antign at multiple sites
• Binding of antibodies is…

  Very specific as each antibody chain is made up from different gene segments
• heavy chain classes


  • five different classes (isotopes)
  • IgM, IgG, IgA ,IgD, IgE
  • they differ in structure of H chain
  • different biological activity for each isotope due to structural differences
• Ig classes and subclassses 


  • distinguished by the structure of the constant regions of the heavy chain
  • class determined by heavy chain
  • M,G,A,D,E

  
• Ig classes exist in different forms 


  IgG, IgD and IgE are monomers

  IgA- monomer, dimer

  IgM- pentamer

  
• What is the most abundant immunoglobulin in blood?


  IgG, expressed on the surface of B cells
• What percentage of total serum immunoglobulin does IgG account for?


  80%
• What is the percentage range of IgM in total serum immunoglobulin?


  5-10%
• Where is IgM expressed?


  On the surface of B cells
• What is the function of IgD?


  Function is unknown, co-expresse on the surface of B cells
• What is the predominant immunoglobulin in external secretions?


  IgA
• What is the primary role of IgA?


  Prevent attachment of pathogens to epithelial surfaces
• What does IgE mediate?


  Immediate sensitivity and associated with allergies
• What is IgM 


  low affinity antibody

  complement fixing or complement activating antibody.
• Why is IgM a good agglutinator? (make antibodies stick together) 


  Due to its pentameric form
• What is IgM's effectiveness in neutralizing toxins?


  Not very good at neutralizing toxins or viruses
• What is the role of eosinophils in relation to IgE?


  Attack large parasites using IgE

  but low in levels
• How do eosinophils attack worms?


  Using IgE Fc receptors
• What happens when worms are coated with IgE?


  Eosinophils can attack the worms
• What is the relationship between IgE and mast cells?


  IgE crosslinks mast-cell surface receptors, involved with allergic response
• What type of receptors do mast cells have for IgG?


  High affinity IgG Fc receptors
• What is the role of IgE in allergic reactions?


  It is associated with mediating allergies
• What immunoglobulin (antibody) can cross the placenta 


  IgG (1-4)

  • part of antigenic experience - newborn has protection to all the antigens mother has been exposed to, reflection of antibody memory
• where are antibodies found in the body

  
• effector functions of IgG 


  • high affinity and key for neutralisation of toxins - eg snake venom.
  • IgG neutralise these by blocking their active sites.
  • IgG is an efficient virus neutralising atibody
• IgG Humoral response


  neutralisation of virus by suffocating it - surrounding it.
• how IgG protects cell


  IgG binds with antigenic determinants present on various portions of the virus.

  including the region used by the virus for attachment to the target cell.

  • antibody recognises antigen in its native state .
  • protects cell by blocking binding of toxin to receptors on cell surface
• how do viruses develop


  by binding to B cell receptors- under go endocytosis and use host machinery to make more viral particles
• Ig most and least efficient for Neutralisation 


  • most- IgG + IgA
  • least - IgE +IgD
• Ig most and least efficient for opsonization 


  • most - IgG1
  • least - IgE, IgD, IgM, IgG2
• ig most and least efficient at activating complement system


  • most - IgM, IgG3
  • least- IgD, IgG4 + IgE
• ig most and least efficient at sensitization of mast cells 


  • most - IgE
  • least - IgM, IgD, IgG, IgA