Lecture 3 Antibody-Antigen Reactions Binding of the epitope in the antigen binding site



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Lecture 3 Antibody-Antigen Reactions


Binding of the epitope in the antigen binding site



Antibody Avidity

  • Multiple interactions between antigen binding sites and epitopes

  • Greater than additive

  • Similar to Velcro™

  • More relevant to biologic systems than affinity



Effect of multivalent interactions



Biological Consequences of Antibody Affinity/Avidity

  • Neutralization of toxins

  • Complement activation

  • Immune elimination of antigen

  • Virus neutralization

  • More intense immune complex disease in animals

    • higher levels of circulating antigen-antibody complexes
    • more intense localization of immune complexes on basement membranes.
    • more severe impairment of organ function


Cross-Reaction



Antigen-Antibody Interactions

  • Quality and quantity are important in resolution of disease

  • May contribute to pathology

  • Useful in immunological assays



Immune Precipitation



Agglutination



Enzyme (ELISA) Immunoassay



Complement activation

  • A system of plasma proteins that interact with

    • Antigen/antibody complexes
    • Pathogen surface motifs (alternative and lectin pathways
  • Activation of complement results in

    • Chemo-attraction of inflammatory cells
    • Peptide mediators of inflammation (anaphylatoxins)
      • Increased blood vessel permeability
      • Smooth muscle contraction
      • Mast cell degranulation
    • Opsonization of pathogens (enhances phagocytosis)
    • Killing of pathogens (membrane attack complex)


Overview of the Complement Cascade



Effector Actions of Complement



Terms to remember

  • Affinity

  • Agglutination

  • Avidity

  • Complement

    • Classical pathway
    • Alternative (properdin) pathway


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