immunity

• Communicable/infectious disease

  Caused by pathogens, Contagious
• Pathogen

  Organism capable of causing disease
• Types of pathogens

  • Bacteria
  • Viruses
• Bacteria

  • Many non-pathogenic bacteria, Single celled, Classified by cell shape
• Bacterial diseases

  • Tetanus (Clostridium tetani)
  • Tuberculosis (Mycobacterium tuberculosis)
  • Whooping cough (Bordetella pertussis)
• Viruses

  • Only visible with electron microscope, Contain EITHER DNA or RNA (never both), Surrounded by protein coat
• Ways pathogens can be transmitted

  • Contact (indirect or direct)
  • Transfer body fluids (saliva, mucus, blood, semen)
  • Infection by droplets
  • Ingestion (of contaminated food or water)
  • Airborne transmission (when droplet has dried up some bacteria and viruses can survive)
  • Vectors
• Non-specific defences

  Work against all pathogens, Body's 'first line' of defence, (external and internal defenses & protective reflexes)
• Specific defences

  Directed at particular pathogen, Immune system produces antibodies to target pathogen
• External defences of the body

  • Skin
  • Mucous membranes
  • Hairs
  • Cilia
  • Acids
  • Lysozyme
  • Cerumen (ear wax)
• Protective reflexes

  • Sneezing
  • Coughing
  • Vomiting
  • Diarrhoea
• Leucocytes (including lymphocytes) and macrophages play a role in defending the body against pathogens
• Inflammation

  Response to tissue damage, Reduce spread, destroy & stop further entry of pathogens, Remove damaged tissue/cell debris, Begin repair of damaged tissue
• Signs of inflammation

  • Redness (increased blood flow)
  • Swelling (movement of fluid from blood into tissue)
  • Heat (increased blood flow)
  • Pain (abnormal conditions stimulate pain receptors)
• Inflammatory response

  1. Mechanical damage/local chemical changes stimulates mast cells to release histamine and heparin

  2. Histamine increases blood flow; also causes increased permeability of blood capillary walls

  3. Heparin prevents clotting in immediate area of injury

  4. Mast cells release chemicals to attract phagocytes

  5. Abnormal conditions stimulate pain receptors

  6. Phagocytes (filled with bacteria/debris/dead cells) begin to die; combines with tissue fluid to form pus

  7. Mitosis in tissue produces new cells (repair occurs)
• Fever

  Elevation of body temperature, Inhibits the growth of some bacteria/viruses, Increases rate of metabolism; helps body cells repair themselves more quickly
• Immune response

  Homeostatic mechanism, Micro-organisms/foreign substances enter body immune response deals with invasion and restores internal environment to normal conditions
• Types of immune responses

  • Antibody-mediated immunity (Humoral response)
  • Cell-mediated response
• Where lymphoid tissue is found

  • Lymph nodes
  • Spleen
  • Thymus gland
  • Tonsils
• Lymphocyte types

  • B cells
  • T cells
• Antigen

  Any substance capable of causing a specific immune response, Causes body to produce antibodies, Large molecules; proteins, carbohydrates, lipids or nucleic acids
• Self-antigen

  Large molecules; produced by own body, Do not cause immune response
• Non-self-antigen


  'Foreign' compounds, Do cause immune response
• Antibody plasma cells

  1. cells produced from specific cloned B-cell, Produces specific antibodies which will act on pathogen
• Memory cells

  Cells which remain in body for long time (sometimes > 20 years), Enable immune response to be activated quickly should pathogen enter body again
• Antibody-mediated immunity (humoral response)

  1. Pathogen enters the body

  2. Macrophage engulfs pathogen

  3. Macrophages present the non-self antigen / fragment

  4. B cells activate, enlarge & divide into clone cells

  5. Most clone cells become plasma cells that secrete a specific antibody capable of attaching to an active site of an antigen

  6. Antibodies circulate blood, lymph & extracellular fluid – reach infection site

  7. The remaining clone cells become memory cells & remain in the body for a long time

  8. Memory cells spread to all body tissues – allows response to occur more rapidly
• Ways antibodies may render an antigen inactive

  • Antibody combines with foreign enzymes/bacterial toxins - Inactivate them by inhibiting reaction with other cells or compounds
  • Bind to surface of virus; prevent entry into cell
  • Coat pathogens; enhances consumption by phagocytes
  • Cause agglutination – antibodies cause pathogens to clump together, easier for phagocytes to destroy
  • Dissolve organisms (Lysis)
  • React with soluble substances to make them insoluble - More easily consumed by phagocytes (Precipitation)
• B cells activate, enlarge & divide into clone cells

  1. B cells activate

  2. B cells enlarge

  3. B cells divide into clone cells
• Most clone cells become plasma cells that secrete a specific antibody capable of attaching to an active site of an antigen

  1. Clone cells become plasma cells

  2. Plasma cells secrete specific antibody

  3. Antibody attaches to antigen active site
• Antibodies circulate blood, lymph & extracellular fluid – reach infection site

  1. Antibodies circulate blood

  2. Antibodies circulate lymph

  3. Antibodies circulate extracellular fluid

  4. Antibodies reach infection site
• The remaining clone cells become memory cells & remain in the body for a long time

  1. Clone cells become memory cells

  2. Memory cells remain in body long time
• Memory cells spread to all body tissues – allows response to occur more rapidly

  1. Memory cells spread to all body tissues

  2. Allows rapid response
• Ways antibodies may render an antigen inactive

  • Antibody combines with foreign enzymes/bacterial toxins - Inactivate them by inhibiting reaction with other cells or compounds
  • Bind to surface of virus; prevent entry into cell
  • Coat pathogens; enhances consumption by phagocytes
  • Cause agglutination – antibodies cause pathogens to clump together, easier for phagocytes to destroy
  • Dissolve organisms (Lysis)
  • React with soluble substances to make them insoluble - More easily consumed by phagocytes (Precipitation)
• Primary response

  Response upon FIRST EXPOSURE to non self-antigen (pathogen)
• Characteristics of primary response

  • Body response slow; takes several days to build up large amounts of antibodies
  • Takes time for B cells to multiply and differentiate into plasma cells to secrete antibodies, once antibodies reach a peak they start to decline
  • Primary response leaves immune system with 'memory' of pathogen/antigen
• Secondary response

  Second/subsequent exposure to same pathogen/antigen
• Characteristics of secondary response

  • Plasma cells form more quickly; antibody levels rise rapidly
  • Memory cells recognize the antigen more quickly, so antibody levels rise much more quickly in blood and to a higher level that lasts longer
  • Antigen (pathogen) has little chance to exert noticeable effect on body
  • No illness results
• Cell-mediated immunity

  1. Foreign antigen enters the body

  2. Antigen presenting cell present the antigen to a particular type of T-cell

  3. T-cell sensitises, enlarges & divides giving rise to a clone

  4. Some t-cells remain in lymphoid tissues as memory T-cells

  5. Some t-cells don't become memory cells & produce killer t-cells, helper t-cells & suppressor t-cells
• How killer T cells may deal with an invading antigen

  1. Migrate to infection site

  2. Attach to cells with foreign antigen

  3. Secrete substances that destroy infected cells and go in search of more antigens
• Helper T cells

  • Bind to the antigen on the antigen presenting cells and Secrete cytokines
  • Cytokines attract lymphocytes to the infection which become sensitized and activated intensifies response
  • Attract macrophages to infection site
  • Intensify phagocytic activity of macrophages
  • Promote the action of Killer T-cells