the immune system

• describe antigens

  proteins on the surface of all cells which signal to immune system any foreign cells
• describe the stages of the immune response

  1. phagocytosis and presentation of foreign pathogens
  2. activation of T cells (helper and cytotoxic)
  3. activation of B cells (divides into plasma cells)
  4. production of antibodies
• describe phagocytosis

  1. antigens bind to the receptors on the cell surface of phagocytes
  2. the phagocyte engulfs the pathogen in a phagosome
  3. a lysosome fuses with the phagosome to form a phagolysosome , and releases hydrolytic enzymes which digest the pathogen
  4. the pathogen's antigens are transported to the cell surface membrane of the phagocyte, this triggers other cells in the immune response
• what activates the T helper cells in the immune response

  the presentation of pathogen antigens in phagocytosis
• what do cytotoxic T cells do?

  release toxins which bind to and kill foreign cells/pathogens in the body
• which cells make antibodies

  B cells
• what is the creation of antibodies from B cells known as

  clonal expansion
• describe agglutination

  the 'clumping' of pathogens together
• how many variable regions does each antibody have?

  two
• how many antigens can one antibody bind to?

  two
• describe the structure of antibodies?

  • two heavy chains and two light chains
  • connected by disulphide bridges
• how does agglutination happen?

  each antibody binds to two antigens
• state two uses of monoclonal antibodies

  • targeted medication e.g. cancer drugs
  • medical diagnosis e.g. pregnancy tests
• what does the ELIZA test stand for?

  enzyme-linked immunosorbent assay
• describe the process of ELIZA testing

  1. antigens are fixed to the bottom of a well plate
  2. a sample of the blood being tested is added to the plate
  3. the beaker is washed to remove any unbound antibodies
  4. secondary antibodies which are bound to an enzyme are added
  5. a solution is added which causes the enzyme to change colour if these antibodies bind
• which cells are produced by T and B cells after a primary infection

  memory cells
• state two differences between the primary and secondary immune responses

  • secondary is quicker
  • no symptoms are shown in the secondary response
• what do vaccines contain?

  dead or weakened versions of pathogens
• describe herd immunity

  the idea that if enough people in a community are vaccinated and have immunity, everyone is less likely to become infected
• what are the two forms of immunity?

  active and passive
• describe passive immunity

  an individual receives antibodies from an external source- they are not created by themselves
• describe active immunity

  when the individual has created their own antibodies
• describe the structure of HIV

  • a capsid which contains genetic material (RNA) and enzymes (reverse transcriptase and integrase)
  • viral envelope
• describe how HIV infects T-helper cells

  1. HIV attachment proteins bind to receptors on the surface of helper T-helper cells.
  2. the viral capsid is injected into the HIV virus, and the enzymes are released
  3. reverse transcriptase converts the viral RNA into double stranded DNA, and the DNA enters the nucleus of T- helper cells.
  4. integrase inserts the HIV DNA into the T-helper cell DNA.
  5. when DNA replication takes place, viral DNA will be replicated and new viruses will be created
• what is aids?

  Acquired Immunodeficiency Syndrome,

  caused when too many T-helper cells have been killed by the HIV virus and the immune system is highly weakened