Antigen-antibody interactions form the foundation of immune responses. These interactions rely on various non-covalent bonds, each contributing to the strength and specificity of the binding. Understanding these bonds is crucial for grasping how antibodies recognize and neutralize threats.

Immunoassays harness antigen-antibody interactions for practical applications. Techniques like ELISA and Western blot enable disease diagnosis, vaccine development, and therapeutic interventions. These tools have revolutionized medical diagnostics and treatment strategies across various fields.

Antigen-Antibody Interaction Fundamentals

Types of antigen-antibody bonds

• Non-covalent bonds form basis of antigen-antibody interactions
  • Hydrogen bonds between hydrogen and electronegative atoms contribute significantly in large numbers
  • Van der Waals forces weakly interact between adjacent molecules become significant in close proximity
  • Electrostatic interactions attract oppositely charged ions or regions of molecules stronger than hydrogen bonds
  • Hydrophobic interactions occur between non-polar regions maintain structure of antibody-antigen complexes
• Relative bond strengths from strongest to weakest
  1. Electrostatic interactions
  2. Hydrogen bonds
  3. Hydrophobic interactions
  4. Van der Waals forces

Antibody specificity and cross-reactivity

• Antibody specificity binds particular epitope determined by complementarity determining regions (CDRs)
• Cross-reactivity occurs when antibody binds multiple antigens with similar epitopes
• Factors affecting specificity and cross-reactivity
  • Structural similarity between antigens (hemoglobin variants)
  • Flexibility of antibody binding site adapts to different epitopes
  • Environmental conditions alter binding (pH, temperature, ionic strength)

Immunoassays and Applications

Principles of immunoassays

• Enzyme-Linked Immunosorbent Assay (ELISA) detects antigens or antibodies using enzyme-linked antibodies
  • Types: Direct, indirect, sandwich, and competitive ELISA
  • Applications: HIV testing, food allergen detection, hormone level measurement
• Western blot separates proteins by gel electrophoresis detects with specific antibodies
  1. Sample preparation
  2. Gel electrophoresis
  3. Transfer to membrane
  4. Blocking
  5. Antibody incubation
  6. Detection
  • Applications: HIV confirmation, Lyme disease diagnosis, protein research
• Common immunoassay features
  • Labeled antibodies or antigens (fluorescent, radioactive)
  • Specific antigen-antibody interactions ensure accuracy
  • Signal amplification increases sensitivity (enzyme-substrate reactions)

Applications in vaccines and immunotherapies

• Vaccine development identifies protective antigens elicits specific antibody responses
• Monoclonal antibody therapies target specific antigens in cancer (Herceptin), autoimmune diseases (Humira)
• Passive immunization administers pre-formed antibodies for immediate protection (rabies immune globulin)
• Antibody engineering creates chimeric, humanized antibodies improves efficacy reduces immunogenicity
• Diagnostic applications use antigen-antibody interactions in rapid tests (pregnancy tests, COVID-19 antigen tests)