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

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