immune system

Innate vs. Acquired (Adaptive) Immunity

  • Innate Immunity
    • Definition: Immunity one is born with.
  • Acquired (Adaptive) Immunity
    • Develops upon exposure to antigens.
    • Types of Acquired Immunity:
    • Active Immunity:
      • Definition: Produced by the individual's own immune system.
      • Example: Vaccinations.
    • Passive Immunity:
      • Definition: Transfer of ready-made antibodies.
      • Example: Mother’s milk antibodies.
  • Classifications of Defenses:
    • Non-specific defenses: Innate immunity.
    • Vaccinations: Active acquired immunity.
    • Mother’s milk antibodies: Passive acquired immunity.
    • Environmental exposure: Active immunity through natural exposure.

Immune System Components

  • Key Concepts:
    • Immunocompetent: Ability to mount an immune response.
    • Self-Tolerance: Immune system does not attack the body’s own cells.
  • Important Organ:
    • Thymus: Critical for T cell maturation and development of self-tolerance.
  • Conditions:
    • Normal Health: Immune system functions optimally without attacking self-antigens.
    • Autoimmune Disorders: Immune system mistakenly attacks self-antigens leading to diseases.

Features of Immunity

  • Specificity: The immune response is tailored to specific pathogens.
  • Versatility: Ability of immune system to adapt and respond to a wide range of pathogens.
  • Memory: Long-term immunity from previous infections, leading to faster and stronger responses on re-exposure.
  • Tolerance: Process of ignoring the body’s own antigens.

Lymphocyte Development

  • Lymphocytes: Crucial components of adaptive immunity.
  • Thymus: Site for maturation of T cells.
  • Process of T Cell Production:
    1. Lymphoid stem cells in red bone marrow develop into immature T cells.
    2. Immature T cells migrate to the thymus for maturation.
    3. Thymic hormones facilitate T cell maturation and destruction of self-reactive T cells.
  • Types of T Cells:
    • Helper T Cells (TH): CD4 cells.
    • Cytotoxic T Cells (TC): CD8 cells.
    • Suppressor T Cells (Ts): Regulate immune response.

T Cell Response to Antigens

  • Antigen: Any substance that can induce an immune response; derived from the phrase "antibody generating."
  • Definition of Antigens:
    • Usually peptides, but can include carbohydrates, lipids, and metals. Haptens are small antigens that become immunogenic only when attached to carriers.
  • T Cell Activation:
    • T cells possess receptors specific for antigens. Activation requires binding of the receptor to the antigenic determinant on the antigen.

MHC (Major Histocompatibility Complex)

  • MHC Class I Molecules:

    • Present on nearly all nucleated cells.
    • Present endogenous antigens to cytotoxic T cells (TC cells).
    • Indicate abnormal cell status to the immune system (e.g., cancer, virus-infected).

  • MHC Class II Molecules:

    • Present only on antigen-presenting cells (APCs) such as macrophages and dendritic cells.
    • Present exogenous antigens to Helper T cells (TH cells).

  • Antigen Processing:

    • Endogenous: Synthesized inside the cell, processed by MHC Class I.
    • Exogenous: Taken up by phagocytosis, processed by MHC Class II.

T Cell Activation and Clonal Selection

  • T Cell Interaction: TH cells interact with MHC Class II, TC cells interact with MHC Class I.
  • Activation Mechanism:
    • Requires cytokines and interleukin-2 (IL-2) for TC cell activation.
    • TH cells help in the activation of B cells and other immune responses via cytokine secretion.

Effects of T Cells

  • Helper T Cells (TH):
    • Activate macrophages, trigger B cell proliferation, and secrete various interleukins.
    • Enhance phagocytosis and coordinate the immune response.
  • Cytotoxic T Cells (TC):
    • Function to destroy infected or abnormal cells by releasing perforin and enzymes, inducing apoptosis in target cells.

B Cell Immunity

  • B Cells Circulation:
    • Have antibodies on their surface; naïve B cells identify matching antigens for activation.
    • Activated B cells differentiate into:
    • Effector B Cells (Plasma Cells): Produce antibodies.
    • Memory B Cells: Provide long-term immunity.

B Cell Activation, Clonal Selection, and Differentiation

  • Activation Process:
    1. Binding of B cell receptor to antigen.
    2. Interaction with Helper T cells and cytokines triggers division.
    3. Results in plasma cells that secrete antibodies and memory B cells.

Antibodies: Structure and Function

  • Structure of Antibodies:
    • Composed of monomeric units; variable regions specific to antigens.
  • Functions:
    • Agglutination: Clumping antigens for easier phagocytosis.
    • Neutralization: Blocking pathogen effects, i.e., viral binding sites.
    • Complement Activation: Leads to pathogen lysis, enhances inflammation.

Immunological Memory

  • Primary vs. Secondary Immune Response:
    • Primary Response:
    • Lag phase: 4-5 days, peak response at 7-14 days, primarily IgM antibodies.
    • Secondary Response:
    • Quicker (1-3 days), stronger IgG antibody response.

Immune Disorders

  • Types of Immune Disorders:
    • Hypersensitivity Disorders: Overreaction of the immune system leading to tissue damage.
    • Immunodeficiency Disorders: Failures in immune components (e.g., HIV).
    • Autoimmune Disorders: Immune system attacks self-antigens (e.g., lupus).

Autoimmune Disorders

  • Characteristics: Autoimmunity may lead to a range of diseases affecting different systems:
    • Endocrine System: Graves' Disease, Hashimoto's thyroiditis.
    • Neurological System: Multiple Sclerosis, Guillain-Barre Syndrome.
    • Gi Tract: Celiac Disease, Crohn's Disease.