Chapter 18: Practical Applications of Immunology

Vaccines

Vaccines are biological preparations that provide acquired immunity to specific infectious diseases. They stimulate the immune system to recognize and combat pathogens.

• Bacterial Vaccines: Examples include DTaP (Diphtheria, Tetanus, Pertussis), Toxoid vaccines (inactivated toxins), and conjugated vaccines (e.g., Haemophilus influenzae type B).

• Viral Vaccines: Examples include polio (inactivated and oral), influenza, MMR (measles, mumps, rubella), and HPV.

• Subunit Vaccines: Contain purified antigens (e.g., acellular pertussis, hepatitis B).

• Conjugated Vaccines: Combine weak antigens with strong protein carriers to enhance immune response (e.g., Hib).

• Recombinant Vaccines: Use genetically engineered antigens (e.g., hepatitis B).

• Active Immunity: Immunity developed after exposure to antigen via infection or vaccination.

• Passive Immunity: Immunity acquired by transfer of antibodies (e.g., maternal antibodies, antitoxin injections).

Example: The polio vaccine is available in two forms: inactivated (IPV) and oral (OPV). IPV is safer but less effective at inducing gut immunity compared to OPV.

Types of Immunity

• Active Immunity: Body produces its own antibodies after exposure to antigen.

• Passive Immunity: Antibodies are transferred from another source (e.g., mother to fetus via placenta).

• Natural Immunity: Acquired through natural exposure to pathogens.

• Artificial Immunity: Acquired through medical intervention (e.g., vaccination, antibody therapy).

Additional info: Passive immunity provides immediate protection but is short-lived, while active immunity is long-lasting but takes time to develop.

Chapter 18: Review Questions

Vaccine Components and Types

• DTaP Vaccine: Contains diphtheria and tetanus toxoids, and acellular pertussis antigens.

• Subunit Vaccines: Use only parts of the pathogen to stimulate immunity.

• Conjugated Vaccines: Combine polysaccharides with proteins to enhance immunogenicity.

Example: The Hib vaccine is a conjugated vaccine that protects against Haemophilus influenzae type B.

Advantages of Passive Immunization

• Provides immediate protection.

• Useful for immunocompromised individuals or post-exposure prophylaxis.

Chapter 19: Hypersensitivity

Types of Hypersensitivity

Hypersensitivity reactions are exaggerated or inappropriate immune responses to antigens, classified into four types.

• Type I (Anaphylactic): Rapid allergic reactions mediated by IgE antibodies. Examples: food allergies, hay fever, asthma.

• Type II (Cytotoxic): Antibody-mediated destruction of cells. Examples: ABO blood transfusion reactions, hemolytic disease of the newborn.

• Type III (Immune Complex): Immune complex deposition causes inflammation. Examples: serum sickness, Arthus reaction.

• Type IV (Delayed-Type): T-cell mediated responses. Examples: contact dermatitis, tuberculin skin test.

Type I Hypersensitivity: Mechanism and Examples

• Mechanism: Allergen binds to IgE on mast cells, causing release of histamine and other mediators.

• Symptoms: Bronchial swelling, edema, shock (anaphylaxis).

• Example: Peanut allergy causing rapid onset of symptoms.

Type II Hypersensitivity: Cytotoxic Reactions

• Mechanism: IgG or IgM antibodies bind to cell surface antigens, leading to cell destruction via complement activation.

• Examples: Hemolytic disease of the newborn, transfusion reactions.

Type III Hypersensitivity: Immune Complex Reactions

• Mechanism: Antigen-antibody complexes deposit in tissues, causing inflammation.

• Examples: Arthus reaction, serum sickness.

Type IV Hypersensitivity: Delayed-Type Reactions

• Mechanism: Sensitized T cells release cytokines, attracting macrophages and causing tissue damage.

• Examples: Allergic contact dermatitis (e.g., poison ivy), tuberculin skin test (Mantoux test).

• Mantoux Test: Used to diagnose tuberculosis exposure; positive result indicates prior sensitization.

Additional info: Type IV reactions are important in organ transplant rejection and autoimmune diseases.

Tables

Comparison of Hypersensitivity Types

Key Equations

• Rate of Immune Response:

• Antibody Titer Calculation:

Summary

• Vaccines are essential tools for preventing infectious diseases and can be classified by their components and mechanisms.

• Hypersensitivity reactions are classified into four types based on immune mechanisms and clinical manifestations.

• Understanding these concepts is crucial for clinical practice and immunological research.