Antibodies/Adaptive Immune System

Overview of the Immune System

  • Immune System Components

    • The immune system consists of two main components: the innate immune system and the adaptive immune system.

Innate Immune System

  • Definition: The innate immune system is the part of the immune system that is present at birth and functions similarly across all individuals.

  • Characteristics:

    • Works the same in everyone who has a normal immune system.

Adaptive Immune System

  • Definition: The adaptive immune system develops throughout life as individuals are exposed to different pathogens.

  • Characteristics:

    • Unique to each individual due to differences in exposures to antigens.

    • Interacts specifically with pathogens through the effects of antigens and antibodies.

Antigens and Antibodies

  • Antigen:

    • Full name: antibody generator.

    • Definition: Any substance that enters the body and triggers the production of antibodies.

    • Epitopes: Specific regions on antigens where antibodies bind.

  • Examples of Antigens:

    • Viruses and bacteria entering the human body prompt the immune response.

Function of Antibodies

  • Definition: Proteins produced by the immune system in response to antigens.

  • Structure of Antibodies:

    • Y-shaped structure consisting of four subunits:

    • 2 small (light) chains

    • 2 larger (heavy) chains

    • Held together by disulfide bonds between cysteine residues.

  • Regions of Antibodies:

    • Variable region: Where the antibody binds to specific antigens.

    • Constant region: Does not bind to antigens; helps in phagocytosis by binding to receptor proteins on pathogens.

Classes of Antibodies

  1. IgG:

    • Most abundant, longest-lived, crucial for secondary immune response.

    • Important for future immunity as it is passed from mother to fetus through the placenta.

    • Lifespan: 21 days.

  2. IgM:

    • Important in primary immune response; primarily found in blood.

    • Lifespan: 10 days.

  3. IgA:

    • Protects mucosal areas, such as the intestines.

    • Lifespan: 6 days.

  4. IgD:

    • Involved in the activation of B cells.

    • Lifespan: 3 days.

  5. IgE:

    • Plays roles in allergic reactions and defense against parasites.

    • Lifespan: 2 days.

Functions of Antibodies

  • There are six primary functions of antibodies:

    1. Neutralization: Binding to pathogens to block their ability to infect cells.

    2. Opsonization: Coating pathogens to enhance phagocytosis.

    3. Immobilization: Preventing pathogens from moving freely, making them easier to target.

    4. Complement activation: Assisting in the activation of the complement system for immune responses.

    5. Agglutination: Clumping of pathogens to simplify their removal by immune cells.

    6. Natural Killer (NK) cell activation: Engaging NK cells for additional immune actions.

B Cells and Antibody Production

  • B Cells: The only cells that can produce antibodies. Each B cell produces unique antibodies via alternative splicing of genes.

  • Activation of B Cells:

    • When B cells bind to their specific antigens, they begin to proliferate and differentiate into two types:

    • Memory cells: For faster responses in future encounters with the same antigen.

    • Plasma cells: Produce and release antibodies into circulation.

  • Role of T Cells:

    • T Helper Cells: Activate B cells and macrophages through cytokines.

    • T Cytotoxic Cells: Destroy infected or cancerous cells directly through apoptosis.

Immunization and Immunity

  • Active Immunity: When the body produces antibodies through natural infection or vaccinations (attained through exposure to an antigen).

    • Natural: Immunity from past infections.

    • Artificial: Vaccination, where antibodies are produced deliberately.

  • Passive Immunity: Antibodies are given to an individual without requiring the individual to produce them.

    • Natural: Maternal antibodies (IgG from placenta, IgA from breast milk).

    • Artificial: Injection of pre-made antibodies (e.g., immunoglobulin treatments).

Types of Vaccines

  • Attenuated Vaccines: Weakened form of pathogens that still replicate but do not cause disease; typically requires only one dose.

  • Inactivated Vaccines: Killed pathogens that do not replicate or spread; usually need booster shots to maintain immunity.

  • Subunit Vaccines: Contain pieces of the pathogen (e.g., specific proteins) instead of the whole organism.

  • Toxoid Vaccines: Involve inactivated toxins from bacteria, prompting an immune response without causing disease.

  • Polysaccharide Vaccines: Based on polysaccharides from the surface of bacteria, effective in targeting specific bacterial infections.

Importance of Vaccines

  • Vaccines develop immunity without causing the disease itself, significantly reducing health risks associated with infections.

  • It is crucial to distinguish between active and passive immunity when discussing vaccination schedules and health protocols, particularly in emergency scenarios where immediate immune response is needed.

Historical Context

  • Discussion on the history of vaccination and diseases like polio will provide additional insight into the impacts and relevance of immunization practices.