Humoral Immune Response

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Humoral Immune Response

• Terry Kotrla, MS, MT(ASCP)BB
• Fall 2006

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Humoral Immunity

• Results in production of proteins called
  immunoglobulins or antibodies.
• Body exposed to foreign material termed
  antigen which may be harmful to body virus,
  bacteria, etc.
• Antigen has bypassed other protective mechanisms,
  ie, first and second line of defense.

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Dynamics of Antibody Production

• Primary immune response
• Latent period
• Gradual rise in antibody production taking days
  to weeks
• Plateau reached
• Antibody level declines

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Dynamics of Antibody Production

• Antibody production
• Initial antibody produced in IgM
• Lasts 10-12 days
• Followed by production of IgG
• Lasts 4-5 days
• Without continued antigenic challenge antibody
  levels drop off, although IgG may continue to be
  produced.

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Secondary Response

• Second exposure to SAME antigen.
• Memory cells are a beautiful thing.
• Recognition of antigen is immediate.
• Results in immediate production of protective
  antibody, mainly IgG but may see some IgM

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Humoral Immune Response
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Dynamics of Antibody Production
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Cellular Events

• Antigen is processed by T lymphocytes and
  macrophages.
• Possess special receptors on surface.
• Termed antigen presenter cell APC.
• Antigen presented to B cell

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Basic Antibody Structure

• Two identical heavy chains
• Gamma
• Delta
• Alpha
• Mu
• Epsilon

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Basic Antibody Structure

• Two identical light chains
• Kappa OR
• Lambda

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Basic Antibody Structure
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Basic Structure of Immunoglobulins
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Papain Cleavage

• Breaks disulfide bonds at hinge region
• Results in 2 fragment antigen binding (Fab)
  fragments.
• Contains variable region of antibody molecule
• Variable region is part of antibody molecule
  which binds to antigen.

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Papain Cleavage
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Pepsin

• Breaks antibody above disulfide bond.
• Two F(ab)2 molecules
• The rest fragments
• Has the ability to bind with antigen and cause
  agglutination or precipitation

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Papain and Pepsin Cleavage
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IgG

• Most abundant
• Single structural unit
• Gamma heavy chains
• Found intravascularly AND extravascularly
• Coats organisms to enhance phagocytosis
  (opsonization)

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IgG

• Crosses placenta provides baby with immunity
  for first few weeks of infants life.
• Capable of binding complement which will result
  in cell lysis
• FOUR subclasses IgG1, IgG2, IgG3 and IgG4

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IgG
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IgA

• Alpha heavy chains
• Found in secretions
• Produced by lymphoid tissue
• Important role in respiratory, urinary and bowel
  infections.
• 15-10 of Ig pool

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Secretory IgA

• Exists as TWO basic structural units, a DIMER
• Produced by cells lining the mucous membranes.

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Secretory IgA
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IgA

• Does NOT cross the placenta.
• Does NOT bind complement.
• Present in LARGE quantities in breast milk which
  transfers across gut of infant.

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IgM

• Mu heavy chains
• Largest of all Ig PENTAMER
• 10 of Ig pool
• Due to large size restricted to intravascular
  space.
• FIXES COMPLEMENT.
• Does NOT cross placenta.
• Of greatest importance in primary immune response.

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IgM
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IgE

• Epsilon heavy chains
• Trace plasma protein
• Single structural unit
• Fc region binds strongly to mast cells.
• Mediates release of histamines and
  heparingtallergic reactions
• Increased in allergies and parasitic infections.
• Does NOT fix complement
• Does NOT cross the placenta

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IgE
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IgD

• Delta heavy chains.
• Single structural unit.
• Accounts for less than 1 of Ig pool.
• Primarily a cell bound Ig found on the surface of
  B lymphocytes.
• Despite studies extending for more than
  4 decades, a specific role for serum IgD has not
  been defined while for IgD bound to the membrane
  of many B lymphocytes, several functions have
  been proposed.
• Does NOT cross the placenta.
• Does NOT fix complement.

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Cellular Immune Response

• Important in defending against fungi,
  parasites, bacteria.
• Responsible for hypersensitivity, transplant
  rejection, tumor surveillance.
• Thymus derived (T) lymphocytes

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Cell Mediated Reaction

• Helper T cells turn on immune response
• Suppressor T cells turn off immune response
• Cytotoxic T cells directly attack antigen

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Cell Mediated Immunity
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Lymphokines
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Summary

• http//www.biology.arizona.edu/immunology/tutorial
  s/immunology/page2.html

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• http//www.jdaross.cwc.net/humoral_immunity.htm
• http//academic.brooklyn.cuny.edu/biology/bio4fv/p
  age/aviruses/cellular-immune.html
• http//www.uic.edu/classes/bios/bios100/lecturesf0
  4am/lect23.htm