Immunity

• Parts of the immune system

  • Specific
  • Non-specific
• Non-specific immune system


  • Skin as first line of defense
  • Mucus linings
  • Acidic environments
  • Macrophages
  • Neutrophils
  • Complement proteins
• Phagocytosis


  1. Chemotaxis

  2. Opsonins

  3. Phagocyte receptors

  4. Phagosome formation

  5. Phagolysosome formation

  6. Digestion
• Antigen


  Molecule that causes the formation of an antibody

  
• Antibody


  Globular glycoprotein belonging to a class of plasma proteins called immunoglobulins

  
• Antibody structure


  • Four polypeptide chains
  • Two heavy chains
  • Two light chains
  • Disulphide bonds
  • Two identical antigen binding sites
  • Variable region
  • Constant region
  • Hinge region

  
• How antibodies work


  1. Agglutination

  2. Immobilisation

  3. Prevention of entry into cells

  4. Neutralisation of toxins

  5. Lysis of bacterial cells

  6. Coating/labelling pathogens

  
• Parts of the specific immune system

  • Cell-mediated immune response
  • Humoral immune response
• Maturation of B cells

  1. Develop B-cell/antibody receptor molecules

  2. Genetically programmed to produce over 10 million variants

  3. Activated B cells produce different antibodies (polyclonal response)

  
• Maturation of T cells

  1. Develop into thymocytes

  2. Develop CD4 or CD8 receptors

  3. CD4 cells become T helper cells

  4. CD8 cells become cytotoxic T cells or T suppressor cells
• T helper cells are key to launching an immune response
• HIV targets and destroys T helper cells, compromising the immune system
• Cell-mediated immune response


  1. Cytotoxic T cells detect and destroy virally infected cells and cancer cells

  2. Produce interferon to inhibit viral replication
• Regulation of immune response

  T suppressor cells decrease activity of white blood cells to return to normal alertness level
• Types of immunity


  • Natural active
  • Natural passive
  • Artificial active
  • Artificial passive
• Natural active immunity


  Immune response from natural infection, producing antibodies and memory cells
• Artificial active immunity


  Immune response stimulated by vaccination, producing antibodies and memory cells
• Level


  Protein synthesis, nutrients etc.
• One would want the system to go back to the normal level of alertness
• T suppressor cells


  Bring the immune system back to a normal level of alertness
• Lymphokines


  Secreted by T suppressor cells, decreases the activity of all the white blood cells that were involved
• Types of immunity


  • Natural - active or passive
  • Artificial - active or passive
• Natural active immunity


  • Happens as a result of natural infection
  • Undergo the immune response, humoral and cell mediated
  • Produce antibodies which fight the pathogen
  • Create memory cells which enable immunological memory
• Artificial active immunity


  • Basis for vaccination/immunisation
  • Antigen is purposely injected into the body to stimulate the immune response
  • Body undergoes humoral and cell-mediated responses and creates memory cells
  • Preparations containing the antigen are called vaccines
  • Administering the vaccine is called vaccination
• Natural passive immunity


  • Antibodies are introduced to the fetus from the mother
  • Maternal antibodies cross the placenta and enter the fetus
  • Immune system of the fetus is not fully developed in the first few months
  • First few days of milk (colostrum) are rich in antibodies
• Artificial passive immunity


  • Antibodies/Antitoxins must be injected in the blood to combat the infective agent immediately
  • Horses are injected with a mild form of the toxin, produce the antibodies/antitoxins which can be extracted and purified for use
  • Antibodies do not last long in the body, one must get a vaccination to build up their own immunity
• Vaccine


  A biological preparation containing antigenic material that provides artificial active immunity to a particular disease, made from weakened/killed form of pathogen, toxins or surface proteins/antigens
• Attenuated organism


  • Treated to remove the virulence, still alive but relatively harmless
  • Injected into the body to stimulate the primary immune response
• Dead organism vaccine


  • Can stimulate an immune response but not as efficient as a live organism
  • If not properly treated, can actually infect the person with the disease
• Ways to prepare vaccines

  • Killing the organisms
  • Using a live organism
  • Toxoids
• Killing the organism vaccine

  • Organism is killed in a way that the antigenic properties remain intact
• Live/attenuated organism vaccine


  • Organism is crippled so it does not retain pathogenicity, can still multiply but not very fast
• Toxoid vaccine


  • Inactivated toxins, detoxified by chemicals like formaldehyde to remove toxicity but retain antigenic properties
• Modern trend will be to produce vaccines by genetic engineering, extracting and inserting specific antigen proteins into bacteria for mass production
• Antibiotic


  A chemical substance produced or derived from microorganisms that can destroy or inhibit the growth of other microorganisms
• Key ways antibiotics work

  • Target cell wall synthesis
  • Inhibit protein synthesis, transcription and translation
  • Disrupt cell membrane functions
  • Interfere with or disrupt enzyme action
• Sulfonamides (sulfa drugs)


  A group of drugs derived from sulphanilamide that prevents the growth of bacteria
• The key problem with antibiotics is resistance, many bacteria are developing resistance
• Antibiotics should only be prescribed as a last resort, continuous use results in the organism developing resistance
• Bacteria can develop resistance through mutation or transfer of resistance from one bacteria to another