ch22 Pt 4

Adaptive Defenses

• Adaptive (Specific) Defenses

  • Triggered by antigen exposure

  • Result from coordinated activities of T cells and B cells

  • Activation requires specific antigens

  • Proliferation occurs via cloning

Lymphocyte Classes

• T Cells (~80% in circulation)

  • Cytotoxic T Cells: Physically and chemically attack antigens

  • Helper T Cells: Activate T cell and B cell responses

  • Regulatory T Cells: Control immune response

  • Memory T Cells: Retain memory of previous antigens and can replicate

• B Cells

  • Differentiate into plasma cells that produce and secrete antibodies

• NK Cells

  • Make up 10-15% of circulating lymphocytes

Types of Adaptive Immunity

• Cell-Mediated Immunity (Cellular Immunity)

  • Provided by cytotoxic T cells

  • Defends against abnormal cells and intracellular pathogens

• Antibody-Mediated Immunity (Humoral Immunity)

  • Provided by B cells

  • Defends against antigens and pathogens in body fluids

Adaptive Immunity Mechanism

• Antigen Presentation

  • Activates immune response via specific defenses

  • Leads to the activation of T and B cells

• Direct Attack Mechanism

  • Activated T cells engage in phagocytosis or release toxins

• Antibody Attack

  • Activated B cells produce antibodies that target pathogens

Antigens in Adaptive Defenses

• Antigens (Ag)

  • Mainly proteins that stimulate immune response when recognized as foreign

  • Activation results in lymphocyte cloning

• Clonal Selection

  • Specificity of antigen leads to the selection of corresponding lymphocyte for cloning

Forms of Immunity

• Adaptive Immunity

  • Acquired after birth

  • Active Immunity: Develops after exposure to antigen

  • Passive Immunity: Antibodies transferred from another source

• Active Immunity Types

  • Naturally Acquired

  • Artificially Acquired

• Passive Immunity Types

  • Naturally Acquired

  • Artificially Acquired

Properties of Adaptive Immunity

• Specificity

• Versatility

• Memory

• Tolerance

T Cell Activation and Antigen Recognition

• T Cell Activation

  • T cells only recognize antigens presented by antigen-presenting cells (APCs)

  • Major Histocompatibility Complex (MHC) proteins present the antigens

• Two Classes of MHC Proteins

  • Class I MHC Proteins

    • Present on all nucleated cells

    • Present intracellular peptides

    • Trigger T cells to destroy abnormal cells

  • Class II MHC Proteins

    • Present on lymphocytes and APCs

    • Present extracellular antigen fragments

Recognition and Response of T Cells

• CD Markers

  • CD8 Markers: Found on cytotoxic T cells, respond to Class I MHC proteins

  • CD4 Markers: Found on helper T cells, respond to Class II MHC proteins

  • CD3 Complex: Activates T cells, present in all T cells

• Antigen Recognition and Costimulation

  • Requires CD8 T cells to encounter a specific antigen on Class I MHC

  • Costimulation is necessary for full activation

Cytotoxic and Memory T Cells

• Cytotoxic T Cells

  • Mobile, seek out and destroy abnormal cells

  • Release perforins and cytokines to trigger apoptosis

• Memory T Cells

  • Remain in circulation for rapid response upon re-exposure to antigens

  • Regulatory T cells inhibit responses of other T and B cells

CD4 T Cells and Cytokines

• CD4 T Cells

  • Activate into helper T cells and memory TH cells

  • Secrete cytokines to support immune responses

• Cytokines

  • Major Groups: Interleukins, interferons, tumor necrosis factors, phagocyte-activating chemicals, colony-stimulating factors

  • Functions: Enhancing immune response and regulating activity of various immune cells

• Interleukins

  • Increase T cell sensitivity to antigens, stimulate B cell activity, suppress immune function

• Tumor Necrosis Factors

  • Slow tumor growth, kill tumor cells, stimulate immune activities

• Cytokine Functions Overview

  • Impact maturity and function of T and B cells, activation of phagocytes and blood cell production