The Lymphatic System and Immunity Chapter 14 Pgs 427-45

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The Lymphatic System and Immunity

• Chapter 14
• Pgs 427-455

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Overview

• Introduction
• Organization of the Lymphatic System
• Functions of the lymphatic system
• Lymphatic vessels
• Lymphocytes
• Lymphoid nodules
• Lymphoid organs
• Lymphatic system and body defenses
• Nonspecific Defenses
• Physical barriers
• Phagocytes
• Immunological surveillance
• Interferons
• Complement
• Inflammation
• Fever

• Specific Defenses The Immune Response
• Forms of immunity
• Properties of immunity
• Overview of immune response
• T cells and cell-mediated immunity
• B cells and antibody-mediated immunity

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Introduction

• Pathogens microorganisms responsible for human
  diseases
• Bacteria
• Viruses
• Fungi
• Parasites
• Lymphatic system
• Keeps us alive and healthy

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Organization of Lymphatic System

• 3 components
• Lymphatic vessels
• Fluid (lymph)
• Lymphoid organs

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Functions of Lymphatic System

• Production, maintenance, distribution of
  lymphocytes
• Respond to presence of
• Invading pathogens
• Abnormal body cells (virus-infected cells, cancer
  cells)
• Foreign proteins (toxins released by bacteria)
• Return of fluid and solutes from peripheral
  tissues to blood
• Distribution of hormones, nutrients, and waste
  products from tissues of origin to general
  circulation

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Lymphatic Vessels
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Types of Lymphocytes

• T cells (Thymus dependent)
• 80 of circulating lymphocytes
• Cytotoxic T cells
• Directly attack foreign cells or body cells
  infected by viruses (cell-mediated immunity)
• Helper T cells
• Stimulate activities of both B and T cells
• Suppressor T cells
• Inhibit both T and B cells

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Types of Lymphocytes

• B cells (Bone-marrow derived)
• 10-15 circulating lymphocytes
• Plasma cells
• Responsible for production and secretion of
  antibodies (immunoglobulins)
• Responsible for antibody-mediated immunity
• NK cells (Natural Killer)
• 5-10
• Attack foreign cells, normal cells infected with
  viruses, and cancer cells
• Immunological surveillance

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Lymphoid Nodules

• Masses of lymphoid tissue w/o a capsule
• Increase and decrease size depending on
  lymphocytes present
• Found beneath epithelial lining of organs in
• Respiratory system
• Digestive system
• Tonsils
• Peyers patches
• Urinary system

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Lymphoid Organs Lymph Nodes
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Lymphoid Organs Thymus
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Lymphoid Organs Spleen
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The Lymphatic System and Body Defenses

• Nonspecific Defenses
• Do not distinguish one threat from another
• Physical barriers
• Phagocytic cells
• Immunological surveillance
• Interferons
• Complement
• Inflammation
• Fever

• Specific Defenses
• Protect against particular threats
• Develop after birth
• Dependent on activity of lymphocytes
• B cells
• T cells

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The Complement System
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Macrophage
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Specific Defense The Immune Response

• Respond to specific antigens
• T cells
• Cell-mediated immunity (cellular immunity)
• Provide defense against abnormal cells and
  pathogens in living cells
• B cells
• Antibody-mediated immunity (humoral immunity)
• Provide a defense against antigens and pathogens
  in body fluids

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Immune System
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Forms of Immunity

• Either innate or acquired
• Innate
• Genetically determined
• Acquired
• Active or Passive
• Active Immunity
• Naturally acquired immunity
• Induced active immunity
• Passive Immunity
• Induced passive immunity
• Natural passive immunity

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Properties of Immunity

• Specificity
• Versatility
• Memory
• Tolerance

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Overview of Immune Response
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T Cells and Cell-Mediated Immunity

• T cells recognize antigens when bound to
  membranes of other cells
• Membrane receptors called major
  histocompatibility complex (MHC) proteins
• 2 classes
• Class I MHC proteins
• Class II MHC proteins

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Class I MHC Proteins

• Found on the surfaces of all of our cells
• MHC proteins bind small peptide molecules
  normally present on cell membrane
• Normal peptides T cell ignores
• Abnormal, virus, or bacteria (nonself) T cell
  activated
• Destroys abnormal/infected cell

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Class II MHC Proteins

• Found only on membranes of lymphocytes and
  phagocytic antigen-presenting cells (APCs)
• Such as monocyte-macrophage group, free and fixed
  macrophages
• Specialized for activating T cells against
  foreign cells and proteins
• Phagocytic APCs engulf and break down foreign
  antigens or pathogens
• Fragments of foreign antigens displayed on
  phagocytic cells membrane
• Bind to Class II MHC proteins
• T cells come in contact and become activated,
  starting the immune response

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T Cells

• T cell activation for both occur when MHC protein
  contains specific antigen T cell programmed to
  detect
• Once activated, T cells divide and differentiate
  in to cells with specific function in immune
  response
• Cytotoxic T cells
• Helper T cells
• Memory T cells
• Suppressor T cells

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Cytotoxic T Cells

• Responsible for cell-mediated immunity
• Activated by exposure to antigens bound to Class
  I MHC proteins
• Activated cells under cell division that produce
  active cytotoxic T cells and memory cells
• Track down and attack bacteria, fungi, protozoa,
  or foreign transplanted tissue

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Cytotoxic T Cells

• Destruction occurs by
• Releasing perforin (destructive protein)
• Ruptures antigenic cell membrane
• Secreting lymphotoxin (poison)
• Kills target cell
• Apoptosis
• Genetically programmed cell death
• T cells activate the genes within the target cell
• Also called Killer T cells

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Apoptosis and Macrophages
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Helper T Cells

• Activated by exposure to antigens bound to Class
  II MHC proteins
• Activated ? divide to produce
• Active Helper T cells and memory cells
• Release variety of cytokines that
• Coordinate specific and nonspecific defenses
• Stimulate cell mediated and antibody-mediated
  immunity

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Memory T Cells

• During cell division for both cytotoxic and
  helper T cells, some develop into memory cells
• Remain in reserve
• If same antigen attacks 2nd time, memory T cells
  immediately differentiate into cytotoxic T cells
  and helper T cells
• Allows for more rapid and effective immune
  response

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Suppressor T Cells

• When activated, depress responses of other T and
  B cells
• Does not occur immediately
• Takes much longer for these cells to become
  activated
• Act after initial immune response

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B Cells and Antibody-Mediated Immunity B Cell
Activation

• Each B cell carries its antibody molecules in its
  cell membrane
• If ISF contains antigens that can bind to
  antibodies, B cells become sensitized
• Antigens enter B cell and become displayed on
  Class II MHC proteins on surface of B cell
• Helper T cell activated by same antigen attaches
  to MHC protein-antigen complex and secretes
  cytokines that
• Promote B cell activation
• Stimulate B cell division
• Accelerate plasma cell production
• Enhance antibody production

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B Cell Activation

• Activated B cells divide several times
• Produce daughter cells that differentiate into
• Plasma cells
• Synthesize and secrete large numbers of
  antibodies on surface of sensitized B cells
• Memory cells
• Similar to memory T cells
• If exposed to same antigen, will differentiate
  into plasma cells

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Antibody Structure

• Consist of short and heavy chains of polypeptides
• Each chain has constant and variable segments
• Constant heavy chains form base of antibody
  molecule
• B cells produce only 5 types of constant segments
• Specificity depends on variable segments of light
  and heavy chains
• Free tips contain antigen binding sites (very
  specific for each type of antigen)
• Antigen-antibody complex
• Forms when antibody binds to proper antigen
• Binds to sites and leads to B cell sensitization
  and an immune response

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Classes of Antibodies (Immunoglobins Igs)

• IgG
• Largest and most diverse
• Resist many viruses, bacteria, bacterial toxins
• Can cross placenta
• What type of immunity is that?
• IgM
• Circulate attack bacteria
• IgA
• Found in exocrine secretions
• Ex?
• Attack pathogens before they enter the body
• IgE
• When bound to antigen, stimulates basophils and
  mast cells to release chemicals to stimulate
  inflammation
• IgD
• Attached to B cell and involved in their
  activation

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Antibody Function

• Neutralization
• Agglutination and Precipitation
• Activation of a complement
• Attraction of phagocytes
• Enhancement of phagocytosis
• Stimulation of inflammation

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Primary and Secondary Responses to Antigen
Exposure
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Cool Links!

• Fun immune game
• http//nobelprize.org/medicine/educational/immunit
  y/index.html
• Cool Cytotoxic T cells
• http//www.cellsalive.com/ctl.htm
• Copy and paste them into your browser