Body Defenses and Immune System Notes

  • Immunity

    • Defined as the body's ability to resist or eliminate harmful invaders or abnormal cells.

  • Functions of the Immune System

    • Defend against pathogens (invading bacteria and viruses).
    • Remove worn-out cells and damaged tissues.
    • Immune surveillance: identify and destroy abnormal cancer cells originating in the body.

  • Major Targets of the Immune System

    • Pathogenic bacteria and viruses.
    • Virulence: the disease-producing ability of a pathogen.

  • Leukocytes (White blood cells)

    • The main effector cells in the immune system.
    • Types include neutrophils, eosinophils, basophils, monocytes, and lymphocytes.

  • Lymphoid Tissues

    • Organ sites for lymphocyte production, storage, or processing (e.g., lymph nodes, spleen).
    • Other leukocytes originate from bone marrow stem cells.

  • Types of Immune Responses

    • Innate (Non-specific): Immediate response to foreign material (e.g., inflammation).
    • Adaptive (Specific): Customized responses targeting specific invaders, involving B and T lymphocytes.

  • Components of Innate Immunity

    1. Inflammation:
    • A non-specific response to tissue injury involving phagocytic cells.
    1. Interferon:
    • Proteins that defend against viral infections through viral replication interference.
    1. Natural Killer Cells:
    • Lymphocyte-like cells that destroy virus-infected and cancer cells.
    1. Complement System:
    • Plasma proteins that attack and destroy foreign cells by disrupting their membranes.

  • Process of Inflammation

    • Activated resident macrophages begin phagocytosis of foreign microbes.
    • Vasodilation allows increased blood flow and leukocyte emigration.
    • Increased capillary permeability leads to localized edema.
    • Walling off injured regions to prevent spread and marking bacteria for destruction.
    • Mediated by cytokines, leading to tissue repair.

  • Chronic Inflammation

    • Occurs when the triggering agent persists, relevant to various chronic diseases (e.g., atherosclerosis, asthma).
    • NSAIDs and glucocorticoids can suppress inflammation.

  • Interferon's Role

    • Produced in response to viral attacks; warns neighboring cells to prepare against viruses and enhances NK cell activity.

  • Natural Killer Cells and the Complement System

    • NK cells destroy infected or cancerous cells through membrane disruption.
    • The complement system promotes cell lysis through the formation of the membrane attack complex.

  • Adaptive Immunity

    • Antibody-Mediated (Humoral): B lymphocytes produce antibodies against foreign invaders.
    • Cell-Mediated: T lymphocytes attack unwanted cells directly.
    • B and T lymphocytes originate from stem cells in bone marrow; differentiation is site-dependent (thymus for T cells).

  • Antigen Definition

    • A molecule that triggers an immune response, specifically antibody generation by B lymphocytes.
    • B lymphocytes can respond to T-independent or T-dependent antigens.

  • Antibody Characteristics

    • Y-shaped molecules; specific to unique antigens; consists of heavy and light chains.
    • Effector mechanisms include complement activation, phagocytosis promotion, and NK cell activation.

  • Clonal Selection Theory

    • Proposes that diverse B cells are produced before exposure to antigens.
    • B cells differentiate into plasma cells (secreting antibodies) and memory B cells (for rapid response to future exposures).

  • Types of Immunity

    • Active Immunity: Body produces its own antibodies post-exposure.
    • Passive Immunity: Temporary immunity is gained through pre-formed antibodies.

  • T Lymphocytes

    • Bind directly to their targets when the right antigen-MHC complex is displayed.
    • Types include cytotoxic T cells (destroy infected cells) and helper T cells (enhance immune activity).

  • MHC and Transplant Rejection

    • MHC molecules must be recognized for immune system interaction; mismatches can lead to rejection.

  • Autoimmunity

    • Loss of self-tolerance which can lead to autoimmune diseases (lupus, rheumatoid arthritis).

  • Cancer and Immune Surveillance

    • T cells recognize and destroy potentially cancerous cells to prevent disease progression.

  • Immunodeficiency Diseases

    • Result from insufficient immune responses; examples include severe combined immunodeficiency, which is life-threatening without a sterile environment.

  • Allergies

    • Hypersensitive immune responses against typically harmless substances, varying from mild to severe reactions.