Immune system

• What is a pathogen?

  a disease causing microorganism
• What are the body's physical defences to pathogens?

  Skin

  Membrane linings

  Scilia
• What are the body's chemical defences to pathogens?

  Sweat and oils

  Saliva

  Stomach acid

  Urine

  Tears

  Mucus
• What are phagocytes an example of?

  A non-specific immune response
• What are lymphocytes an example of?

  A specific immune response
• What are the 2 types of lymphocytes?

  T and B cells
• What is an antigen?

  A molecule (often protein) that a body recognises as foreign and so triggers an immune response
• Antigens enable cells to identify...

  Pathogens

  Cells from other organisms

  Abnormal body cells (cancerous)

  Toxins
• Why do scientists have to regularly develop new vaccines for the same disease?

  Lots of pathogens have frequently mutating DNA so any previous immunity will no longer be effective. This is called antigen variability
• What is a phagocyte?

  A phagocyte is a type of white blood cell that carries out phagocytosis (a non-specific immune response)
• What are the stages of phagocytosis?

  • chemicals are released by the pathogen
  • phagocytes are attracted to these chemicals and move towards the pathogen
  • phagocyte engulfs the pathogen into a phagosome
  • lysosomes move towards the phagosome a fuse with it
  • hydrolytic enzymes are released by the lysosomes and digest the pathogen
  • antigens from the pathogen are displayed on the cell surface of the phagocyte
  • this phagocyte is now a antigen presenting cell
• What is an antibody?

  a protein with specific binding sites complementary to a specific antigen synthesised and secreted by plasma cells
• How does an antibody have the shape that it does?

  It has a very specific amino acid sequence which determines its very specific tertiary structure - meaning it can only form antigen antibody complexes with one specific antigen
• What are the 2 regions within an antibody?

  Variable region and constant region
• How do antibodies help with the immune response?

  Antibodies use their 2 specific binding sites to stick 2 pathogens together and then 2 more etc etc in a process of agglutination which makes it easier for phagocytes to locate and engulf pathogens
• Which type of immune response are T cells associated with?

  cell mediated response
• After the T cells have been activated by binding with a phagocyte what 4 functions could it go on to perform?

  • Memory cells
  • Stimulating phagocytosis
  • Becoming cytotoxic killer T cells
  • Helper T cells
• After B cells have been activated by helper T cells what 2 functions could it go on to perform?

  • Memory B cells
  • Plasma cells
• What is the indirect ELISA test?

  The ANTIGEN is bonded to the wells surface
• What is the direct ELISA test?

  The ANTIBODY is bonded to the wells surface
• What are the stages of the ELISA test? (HIV specific)

  • HIV antigen is attached to well in a dish
  • Sample of blood plasma added to the well and if the HIV antibodies are present they will bind to the HIV antigen
  • The well is washed to remove any unbound antibodies. A second antibody with an enzyme attached is added which binds specifically to the HIV antibody
  • The well is washed again to remove any unbound antibodies
  • A yellow solution is then added which turns blue in the presence of the enzyme
  • This will tell if a person is HIV positive
• Why is a control performed in the ELISA test?

  • to ensure only the enzyme is causing the colour change
  • to ensure that washing is effective
• What are the ethics involved in the ELISA test?

  • animal cruelty (cancer in mice)
  • some deaths involved with monoclonal antibody use
  • it is important people are clear on the risks
  • testing the safety of new drugs can be dangerous
• What is direct monoclonal antibody therapy?

  • Specific to antigens on target cells
  • Antibodies are given to a patient
  • Antibodies attach to antigens on cell surface and prevent uncontrolled growth
• What is indirect monoclonal antibody therapy?

  • a cytotoxic drug is attached to the monoclonal antibodies
  • antibodies are given to the patient
  • when the antibody attaches to antigens on the cancer cells it kills the cells
• Describe how a pregnancy test works (positive)

  HCG binds to antibody A and enzyme in reaction site

  HCG and antibody A travel to the test site where antibody B and a substrate are attached

  Antibody B binds to the HCG compounds and keep it there long enough for the enzyme and substrate to react to form coloured dye

  Unreacted antibody As keep travelling to the control site where their enzymes react with the substrate to form another coloured dye
• What is a vaccination?

  Injection of antigens from a pathogen which induces a primary immune response in an individual without them suffering the symptoms of the disease
• What is herd immunity?

  When a sufficiently large enough portion of the population has been vaccinated to make it difficult for a pathogen to spread to those not immunised
• What is antigenic variability?

  a pathogen can mutate frequently which can cause it's surface antigens to change the vaccine then becomes ineffective
• What are the ethical concerns with vaccinations?

  • Use of animals
  • Side effects
  • Who should it be tested on?
  • Should trials only occur in specific countries?
  • Should it be compulsory?
  • Economical concerns
  • Greater good vs individual health risks
• What is passive immunity?

  introducing/inserting monoclonal antibodies into an organism from an outside source - no contact with the pathogen or antigens
• What is active immunity?

  direct contact with the pathogen or its antigens stimulating an immune response to produce its own antibodies
• What are the natural and artificial types of active immunity?

  Natural - infection

  Artificial - vaccination
• What are the natural and artificial types of passive immunity?

  Natural - maternal antibodies

  Artificial - injection of antibodies (anti-venom)
• What are the pros and cons of active immunity?

  Pro - it is longer term because memory cells are created

  Con - it takes longer to develop an immune response
• What are the pros and cons of passive immunity?

  Pro - it is fast acting so you can start fighting the pathogen immediately

  Con - no memory cells are produced and the antibodies break down so it is short term
• What are the features of a successful vaccination?

  • financially viable
  • few side effects - if any
  • must be ways of producing storing and transporting it
  • must be ways of administering the vaccine properly
  • there must be sufficient quantities
• How does HIV replicate?

  • HIV infects a person through bodily fluids into a persons blood
  • Virus binds to the receptor protein CD4 in the surface of T helper cells
  • Viruses lipid envelope fuses with cell surface membrane
  • Capsid breaks down - releasing genetic material and enzymes
  • Reverse transcriptase converts RNA to DNA
  • Viral DNA enters the nucleus through the nuclear pore
  • Viral DNA is inserted into the host cells DNA by integrase
  • HIV DNA is transcribed into mRNA and translated to viral proteins
  • New virus particles are formed and bud off from cell destroying the T helper cell
• What makes a person with HIV have AIDS?

  An uninfected person has 800-1200 T helper cells per mm3 of blood

  When the infected persons count falls below 200 T helper cells per mm3 of blood they then have AIDS
• How do you die from contracting AIDS?

  You don't. AIDS weakens your immune system so much that often people are killed by secondary infections