AntigenAntibody reactions

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Antigen-Antibody reactions
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Antigen-antibody interactions

• Assays detect presence of antigen or antibody
• Used for
• Research
• Diagnosis
• Monitoring humoral immune response
• Therapeutics
• Analysis of interesting molecules

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Noncovalent interactions form the basis for
antigen-antibody binding

• Hydrogen bonds
• Ionic bonds
• Hydrophobic interactions
• Van der Waals interactions
• Weak bonds need many interactions to form a
  strong antigen-antibody interaction

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Nature of antigen-antibody interaction
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Noncovalent interactions operate over a short
distance

• Requires a close fit between antigen and antibody
• Complementarity similar to enzyme substrate
  reactions

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Precipitation reactions

• Antibody and antigen diffuse toward each other
  and precipitate where there is equivalence
• Radial immunodiffusion - quantative
• Double diffusion/Ouchterlony qualitative

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Precipitation reactions

• Measure antibody precipitated versus increasing
  antigen concentration
• Zone of antibody excess
• Antibody not bound detected in supernatant
• Equivalence zone antigen/antibody precipitate
• Zone of antigen excess
• Antigen not bound detected in supernatant

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Precipitation reactions in fluids
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Radial immunodiffusion

• Take a petri dish and fill it with agar and
  antibody
• Cut holes in wells
• Place antigen in wells use different dilutions
• Antigen will diffuse into agar rings will be
  produced at zone of equivalence
• Measure diameter of rings and compare to
  standards
• Can determine the concentration of antigen by
  comparing to a standard curve

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Double immunodiffusion - Ouchterlony

• Both antigen and antibody diffuse forming a
  concentration gradient
• Qualitative assay
• Complexes form lines because both antigen and
  antibody diffuses

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Results for Ouchterlony assay