Adaptive Immune System Summary

  • Definition: Adaptive (acquired) immunity is inducible, specific, systemic, long-lived, and involves memory cells.

  • Characteristics:

    • Inducible: Activated by antigens, not always present.

    • Specific: Targets specific pathogens, ensuring tailored immune responses.

    • Systemic: Immune actions are not confined to the initial infection site; they can affect the entire body.

    • Long-lived Memory: Memory cells allow for a quicker and more potent response upon subsequent exposures to the same pathogen.

  • Immune System Defense Layers:

    1. Surface Barriers: Skin and mucous membranes serve as the first line of defense against pathogens.

    2. Innate Internal Defenses: Includes phagocytes and natural killer cells, which act as the second line of defense.

    3. Adaptive Defenses: Involves humoral (B cells) and cellular (T cells) immunity as the third line of defense, specifically aimed at known pathogens.

  • Adaptive Immune Response Characteristics:

    • Adaptive immunity is specific to pathogens and retains memory for future encounters.

    • Two Arms of Adaptive Immunity:

    • Humoral Immunity: Engements occur via B lymphocytes, which produce antibodies targeting extracellular pathogens.

    • Cell-Mediated Immunity: Involves T lymphocytes that focus on intracellular targets, including virus-infected cells.

  • Lymphocyte Functions:

    • B Cells: Produce antibodies that flag pathogens for destruction and neutralize toxins.

    • Cytotoxic T Cells: Responsible for killing infected or cancerous body cells through direct contact.

    • Helper T Cells: Coordinate the immune response by activating B cells and other T cells, enhancing overall immune activity.

  • Antigens and Antibody Functions:

    • Antigenic Determinants: Specific parts of antigens that induce immune responses from the host.

    • Antibodies: Immunoglobulins (Igs) with versatile functions like opsonization, agglutination, neutralization of toxins, and activating the complement system.

    • Five Outcomes of Antibody Binding:

    1. Opsonization: Marking pathogens for destruction by phagocytes.

    2. Agglutination: Clumping pathogens together to enhance clearance.

    3. Neutralization: Blocking the actions of toxins or viruses.

    4. Complement Activation: Triggering a cascade that leads to pathogen lysis.

    5. Antibody-dependent cytotoxicity: Engaging immune cells to kill the antibody-coated target.

  • Immunological Memory: Specialized memory cells enable a faster and more robust immune response during subsequent exposures to the same pathogen, preventing infections or reducing severity.

  • Types of Immunity:

    • Active Immunity: The body itself produces memory cells, which occurs naturally through infections or artificially through vaccinations.

    • Passive Immunity: Antibodies are received without the body producing memory cells; this can occur naturally (e.g., through breastfeeding) or artificially (e.g., through antibody injections).

  • Hypersensitivity Reactions: Classification of hypersensitive responses:

    1. Type I: Immediate hypersensitivity responses, commonly associated with allergies.

    2. Type II: Cytotoxic reactions, such as blood transfusion reactions.

    3. Type III: Immune complex-mediated conditions like lupus and rheumatoid arthritis.

    4. Type IV: Delayed hypersensitivity, such as contact dermatitis from poison ivy.

  • Conclusion: The adaptive immune system is vital for effective defense against specific pathogens. It features complex interactions among various immune cells, formation of memory for rapid responses, and the potential for hypersensitivity reactions that may impact health adversely.