Notes on Practical Applications of Immunology

Chapter 18: Practical Applications of Immunology

• Antibody Structure

  • Antigen-Binding Site: The specific region on the antibody that directly attaches to an antigen.
  • Heavy Chain and Light Chain: The two types of polypeptide chains that compose an antibody. The heavy chain contains the Fc region, while the light chain pairs with it to form the antigen-binding site.
  • Fc Region: The stem of the antibody that provides mechanisms for immune system interaction.
  • Hinge Region: Allows flexibility in the antibody structure to accommodate the binding of antigens.

• Mechanisms of Antibody Action

  • Agglutination:
    • Definition: Clumping of pathogens or particles, reducing the number of infectious units.
    • Function: A protective mechanism that enhances phagocytosis by making pathogens easier to ingest and destroy.
  • Opsonization:
    • Definition: Coating of pathogens with antibodies to enhance phagocytosis.
    • Outcome: Phagocytes recognize and engulf these antibody-coated microbes more effectively.
  • Neutralization:
    • Definition: Blocking the adhesion of bacteria or viruses to host cells.
    • Example: Preventing toxins from attaching to cells.
  • Complement Activation:
    • Mechanism: Triggers inflammation and cell lysis (destruction).
  • Antibody-Dependent Cell-Mediated Cytotoxicity (ADCC):
    • Process: Antibodies attached to a target cell trigger destruction by immune cells.

• Antibody Titer:

  • Concept: Refers to the concentration of antibodies in the serum, which increases upon initial exposure and further increases with subsequent exposures to the same antigen (e.g., IgM and IgG responses).
  • Graph Representation: Shows the kinetics of antibody response over time, distinguishing between primary and secondary exposures.

• Vaccination:

  • Definition: Introduction of antigens into the body to stimulate an immune response without causing disease.
  • Types of Vaccines:
    • Live, Attenuated Vaccines: Contain weakened pathogens that can replicate, enhancing immune response.
    • Killed/Inactivated Vaccines: Contain dead pathogens; they stimulate the immune response but do not replicate.
    • Subunit/Virus-like Particle Vaccines: Only include parts of the pathogen (e.g., proteins), ensuring safety.
    • Recombinant Vaccines: Use genetically engineered pathogens to produce antigens that safely stimulate an immune response.
    • DNA Vaccines: Introduce plasmids coding for antigens to elicit immunity without presenting the pathogen itself.

• Herd Immunity:

  • Concept: Protection of a population when a significant proportion is immunized, hindering disease spread.
  • Threshold Rates: Different diseases require different immunization rates to achieve herd immunity (e.g., Measles: 83-94%).

• Diagnostic Tests in Immunology:

  • Purpose: Confirm presence of disease, infection, and immune status by detecting pathogens or antibodies.
  • Key Techniques:
    • Monoclonal Antibodies:
      • Definition: Uniform antibodies produced by identical immune cells that are clones of a unique parent cell.
      • Production Process: Involves fusing spleen cells with myeloma cells to create hybridomas that produce specific antibodies.
    • ELISA (Enzyme-Linked Immunosorbent Assay):
      • Types:
        • Direct ELISA: Detects antigens using enzyme-linked antibodies.
        • Indirect ELISA: Detects antibodies in a sample through antigen binding.
        • Sandwich ELISA: Captures antigen with specific antibodies integrated in a sandwich format.
    • Western Blot: Confirmatory test used primarily to diagnose infections like HIV through protein detection.

• Practical Applications: The application of these immunological principles is crucial in vaccine development, disease prevention, and diagnostics in clinical settings.