Immune System and Lymphatic System Lecture Notes

Lymphatic System and Immunity

Overview of the Lymphatic System

  • The lymphatic system plays a critical role in returning lymph to the cardiovascular system.
    • Importance: It ensures fluid balance, filters pathogens, and maintains immune response.

Lymphoid Organs

  • Primary Lymphoid Organs: Bone marrow and thymus, responsible for lymphocyte production and maturation.
  • Secondary Lymphoid Organs: Lymph nodes, spleen, and mucosal associated lymphoid tissues (MALT) that host immune responses.

Immunity

  • Immunity defined as the ability to resist infections.
Three Lines of Defense in Immunity

  1. First Line of Defense (Surface Barriers):

    • Consists of physical barriers: skin, mucous membranes, secretions, and normal flora.
    • Functions to prevent pathogen entry.

  2. Second Line of Defense (Innate Immunity):

    • Nonspecific response involving white blood cells (WBC) and antimicrobial proteins.
    • Components include:
      • White blood cells: Neutrophils, macrophages, dendritic cells, eosinophils, and basophils.
      • Complement system and cytokines.
      • Physiological responses like inflammation and fever.
    • Activation: Occurs within the first 12 hours after pathogen exposure.

  3. Third Line of Defense (Adaptive Immunity):

    • Specific response involving T cells and B cells.
    • Takes 3-5 days to initiate following exposure.
    • Memory formation allows for quicker response upon re-exposure.

Comparison of Innate vs. Adaptive Immunity

  • Innate Immunity:
    • Nonspecific, immediate response, no memory.
    • First and second lines of defense.
  • Adaptive Immunity:
    • Specific, delayed response, memory formation after exposure.

Inflammatory Response

  • Four Cardinal Signs: Redness, heat, swelling (edema), pain.
    • Triggered by inflammatory mediators: Histamine, serotonin, cytokines, bradykinins, prostaglandins, leukotrienes.
    • Increased leukocyte circulation initiates tissue repair and pathogen destruction.

T Cells

  • Types of T Cells:
    • Helper T Cells (TH or CD4): Enhance immune response.
    • Cytotoxic T Cells (TC or CD8): Kill infected or cancerous cells.
T Cell Activation
  • Requires interaction with antigen-presenting cells (APCs) using Major Histocompatibility Complex (MHC) molecules.
    • MHC Class I: Displays endogenous antigens from within the cell; activates TC cells.
    • MHC Class II: Displays exogenous antigens; activates TH cells.
  • Steps to activation:
    1. Binding of T cell receptor to antigen-MHC complex.
    2. Costimulatory signals necessary for full activation.
    3. Clonal proliferation results in memory T cells and effector T cells.

B Cells

  • Function: Activate upon binding to specific antigens via B cell receptors.
  • B Cell Activation:
    • Clonal selection leads to differentiation into plasma cells (produce antibodies) and memory B cells.
  • Types of Antibodies:
    • IgG, IgA, IgM, IgE, and IgD, each serving different immune functions.

Antibody Functions

  • Neutralization: Inhibit pathogen entry and function.
  • Opsonization: Mark pathogens for destruction by phagocytes.
  • Activation of complement system: Promotes pathogen lysis and enhances inflammation.

Vaccination and Immune Response

  • Vaccines stimulate adaptive immunity by introducing antigens, allowing for memory formation and faster responses to future exposures.
  • Differential responses to bacterial vs. viral infections:
    • Bacterial infections often lead to the activation of antibodies.
    • Viral infections typically result in a strong T cell response.

Cancer and the Immune System

  • Immune surveillance involves T cells identifying and destroying cancer cells.
  • Implications if self-reactive T or B cells develop: Potential autoimmunity leading to damage of the host's tissues.

AIDS and Immune Dysfunction

  • AIDS results from the dysfunction of TH cells, severely compromising the immune response and leading to opportunistic infections.