Precipitation and Agglutination Reactions

• What is the main process involved in precipitation reactions?

  Combining soluble antigen with soluble antibody
• Who first noted precipitation reactions and in what year?

  Kraus in 1897
• What must be present for visible precipitation reactions to occur?

  Specific antigen and antibody must fit together
• What do soluble antigens and antibodies produce when combined?

  Insoluble complexes that are visible
• What is required for the reaction between antigen and antibody to occur?

  Multiple binding sites and equal concentrations
• What is affinity in the context of antigen-antibody binding?

  Initial force of attraction between antibody and antigen
• How does cross-reactivity affect antibody reactions?

  Antibodies react with structurally similar antigens
• What happens when the affinity between antigen and antibody is higher?

  Assay reaction becomes more sensitive
• What does avidity represent in antigen-antibody binding?

  Overall strength of antigen-antibody binding
• What is the law of mass action in relation to antigen-antibody reactions?

  Free reactants are in equilibrium with bound reactants
• What is the equilibrium constant formula for antigen-antibody complexes?

  K = K1/K2 = [AgAb]/[Ab][Ag]
• What does K1 represent in the equilibrium constant?

  Forward reaction where antigen binds to antibody
• What does K2 represent in the equilibrium constant?

  Reverse reaction where complex dissociates
• What is the zone of equivalence in precipitation reactions?

  Where equal amounts of antigen and antibody exist
• What occurs in the prozone reaction?

  Excess antibodies prevent visible precipitation
• What is the postzone reaction characterized by?

  Excess antigens with no visible precipitation
• How can precipitation be measured?

  By light scattering techniques
• What does turbidimetry measure?

  Cloudiness of a solution
• What does nephelometry measure?

  Light scattered at a particular angle
• What is the difference between end point and kinetic nephelometry?

  End point measures after completion; kinetic measures immediately
• What is the role of agar and agarose in passive immunodiffusion techniques?

  Stabilize diffusion and visualize precipitin bands
• What factors affect the rate of diffusion in passive immunodiffusion?

  Size, temperature, gel viscosity, hydration
• What is radial immunodiffusion?

  Single diffusion technique with antibody in gel
• What does the end-point method in radial immunodiffusion measure?

  Diameter of the ring at equivalence
• What is the kinetic method in radial immunodiffusion?

  Measures before point of equivalence is reached
• What can cause errors in radial immunodiffusion?

  Overfilling, underfilling, and improper incubation
• What is Ouchterlony double diffusion?

  Both antigen and antibody diffuse independently
• What does a precipitin line forming an arc indicate?

  Serological identity with a common epitope
• What does a pattern of crossed lines in Ouchterlony indicate?

  Two separate reactions with no common epitopes
• What does fusion of two lines with a spur indicate?

  Partial identity with a common epitope
• What does electrophoresis do?

  Separates molecules by electric charge
• What is the purpose of electrophoresis?

  To separate molecules according to charge
• What does fusion of lines at their junction represent?

  Serological identity or common epitope
• What does a pattern of crossed lines indicate?

  Compared antigens share no common epitopes
• What does fusion of two lines with a spur indicate?

  Partial identity between two antigens
• What does the spur in a fusion line point to?

  The simpler antigen
• What is the purpose of electrophoresis?

  Separates molecules by electric charge
• What happens when a direct current is applied in electrophoresis?

  Antigen and antibody migrate in the gel
• What forms as diffusion takes place in electrophoresis?

  Distinct precipitin bands
• What is rocket immunoelectrophoresis?

  One-dimensional electroimmunodiffusion