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• Lymphatic system


  Transport system for cells of the immune system and antigens (foreign substances/cells) to move around the body
• Immune system


  Collection of proteins, cells, tissues and organs widely distributed throughout the body
• Categories of immunity


  • Innate or nonspecific immunity
  • Adaptive or specific immunity

  
• Innate and adaptive immunity are fully integrated in the body

  
• Innate immunity


  • Non-specific defense, present at birth
  • Each time body is exposed to a substance, response is the same (i.e. has no memory)
  • Provides immediate protection from pathogens & antigen

  
• First line of defense in innate immunity


  • Physical barriers
  • exteneral feature

  
• Physical barriers prevent entry or remove microbes

  • Skin
  • Mucous membranes (especially respiratory passageways)
  • Saliva
  • Tears
  • Acid in stomach, urinary tract, vagina
  • Urine flushes urinary passageways
  • Cilia in respiratory tract, coughing and sneezing
• Second line of defense in innate immunity

  • Chemical mediators
  • White blood cells (phagocytes)
  • Inflammation
  • Fever

  
• Chemical mediators


  Promote phagocytosis & inflammation
• Examples of chemical mediators

  • Histamine
  • Cytokines
  • Complement
  • Interferons
• Histamine


  Cause vasodilation, increased vascular permeability, attract white blood cells, stimulate phagocytosis
• Cytokines


  • Secreted by one cell, and stimulates a neighbouring cell to respond
  • Regulate intensity and length of immune response
• Complement


  Stimulate lysis of invading pathogen cells
• Interferons


  Anti-viral activity
• White blood cells in innate immunity

  • Neutrophils
  • Macrophages
  • Basophils
  • Eosinophils
  • Natural Killer Cells
• Neutrophils


  First cell to arrive at a site of insult, acute inflammation; phacocytosis
• Macrophages


  Most effective phagocyte, important in later stages of inflammation & repair; help activate cells of the specific immune system (antigen presenting cell)
• Basophils


  Immunosurveillance; produce histamine (allergy)
• Eosinophils


  Parasitic infection; allergy
• Natural Killer Cells


  Can cause lysis of virus-infected cells or cancer cells
• Components of adaptive immunity

  • B and T lymphocytes

  
• Adaptive immunity


  • Specificity - ability to recognize a particular substance
  • Memory - ability to remember previous encounters with a particular substance and respond rapidly
  • Acquired during lifetime, depending on exposure
  • Fights invaders once innate system is over-run
  • Mediated by lymphocytes (special type of white blood cell) – B & T cells
• Activation of lymphocytes


  1. Lymphocytes (clone of lymphocytes) must recognize antigen

  2. After recognition, lymphocytes must increase in number to destroy antigen
• Types of lymphocytes in adaptive immunity

  • Helper T cells
  • Effector (cytotoxic/killer) T cells
  • B cells

  
• Cell-mediated immunity


  • T lymphocytes
  • Helper T cells
  • Cytotoxic T cells
  • Activated by specific antigen
  • Specific "clones" bind to antigen
  • Co-stimulation required (Helper T cells)
  • Activated cytotoxic T cells divide
• Cytotoxic T cells


  • Eliminate antigen (pathogen)
  • Make holes in cell wall Causes cells to explode
• Antibody-mediated immunity


  • B cells
  • Phagocytosis of an extracellular pathogen that matches the specific B cell receptor on that B cell
  • Require co-stimulation by a Helper T cell that also recognizes the same antigen
  • B cell divides to form
  • Plasma cells – make antibodies
  • Memory B cells – if the same pathogen(antigen) is encountered again, the response is much faster
• Effects of antibodies


  • Inactivate the antigen
  • Bind antigens together
  • Facilitate phagocytosis - an antibody binds to an antigen and then a macrophage which phagocytises the antibody and antigen
• Antibody production


  1. Primary response - When a B cell is first activated by an antigen. B cell proliferates to produce plasma cells (antibody production) and memory cells.

  2. Secondary response - Occurs during later exposure to same antigen. Memory cells divide rapidly to form plasma cells and additional memory cells. Faster and greater response.
• Ways to acquire adaptive immunity

  • Active immunity
  • Passive immunity

  
• HIV = human immunodeficiency virus
• HIV


  • Virus binds to CD4 protein and infects Helper T cells
  • Cells infected with HIV are destroyed by the virus or by immune response
  • Destruction of Helper T cells impairs cell- and antibody- mediated immunity
  • Normal amounts of Helper T's = 1200 cells/mm3
  • When Helper T's get below 200 cells/mm3 acquired immune deficiency syndrome (AIDS)
  • Antibody levels decline and cell mediated immunity is reduced
• When a B cell is first activated by an antigen

  B cell proliferates to produce plasma cells (antibody production) and memory cells
• Secondary response


  1. Occurs during later exposure to same antigen

  2. Memory cells divide rapidly to form plasma cells and additional memory cells

  3. Faster and greater response
• Ways to Acquire Adaptive Immunity

  • Immune Interactions

  
• HIV


  Human immunodeficiency virus
• HIV infection


  1. Virus binds to CD4 protein and infects Helper T cells

  2. Cells infected with HIV are destroyed by the virus or by immune response

  3. Destruction of Helper T cells impairs cell- and antibody- mediated immunity
• Antibody levels decline and cell mediated immunity is reduced
• HIV - AIDS


  • Body is vulnerable and ordinarily infections can be lethal
  • Pneumocystis pneumonia
  • TB, syphilis
  • candidiasis
  • Increased risk of cancer – e.g. Karposi's sarcoma
• pathogens

  foreign agent

  Bacteria

  infection e.g. staphylococcus;

  food poisoning e.g. salmonella Protozoa e.g. amoebaParasites e.g. worms

  Fungi e.g. candida Viruses