The Immune System

• What do foreign antigens trigger?

  an immune response
• what triggers an immune response?

  foreign antigens
• What are antigens?

  molecules/proteins that can generate an immune response when detected by the body
• where are antigens usually found?

  on the surface of cells
• What are antigens used to do?

  used by the immune system to identify:

  • pathogens
  • toxins
  • cells from other individuals of the same species (EG ORGAN TRANSPLANTS)
• What are pathogens?

  microorganisms that cause disease
• in brief terms , what are the four main stages in the immune response?

  1. phagocytes engulf pathogens
  2. phagocytes activate T-cells
  3. T-cells activate B-cells, which divide into plasma cells
  4. Plasma cells make more antibodies to a specific antigen
• What is a phagocyte?


  a type of white blood cell that carries out phagocytosis
• what is phagocytosis?


  engulfment of pathogens
• give an example of a phagocyte?

  a macrophage
• where are phagocytes found?

  in the blood and in tissues
• give one detail about phagocytes?

  they are the first cells to respond to an immune system trigger inside the body
• how do phagocytes work?

  1. A phagocyte recognises the foreign antigens on a pathogen
  2. The cytoplasm of the phagocyte moves round the pathogen, engulfing it
  3. The pathogen is now contained in a phagocytic vacuole in the cytoplasm of the phagocyte
  4. A lysosome fuses with the phagocytic vacuole. The lysozymes BREAK DOWN the pathogen
  5. The phagocyte then presents the pathogen's antigens- it sticks the antigens on its surface to activate other immune system cells
• what does a phagocyte recognise?

  the foreign antigens on a pathogen
• how does the phagocyte engulf the pathogen?

  the cytoplasm of the phagocyte moves round the pathogen, engulfing it
• what do phagocytes activate?

  T-cells
• what is a t-cell a type of?

  white blood cell
• what are T-cells also called?


  T-lymphocytes
• What do T-lymphocytes have?

  Receptor proteins on their surface that bind to complementary antigens presented to it by phagocytes.

  This ACTIVATES the T-cell
• How do different types of T-cells respond?

  in different ways
• what are T-lymphocytes also called?

  T-cells
• give two types of T-cells?

  helper T-cells

  Cytotoxic T-cells
• How do helper T-cells respond?


  They release chemical signals that activate and stimulate phagocytes

  Helper T-cells also activate B-cells which secrete antibodies
• how to cytotoxic T-cells respond?


  They kill abnormal and foreign cells
• what are Th cells?


  HELPER T-CELLS
• WHAT ARE Tc cells ?

  cytotoxic t cells
• what do t-cells activate?


  B-cells
• what are B-cells a type of?

  white blood cell
• what are B-cells also called?


  B-lymphocytes
• what are B-lymphocytes also called?

  B-cells
• what are B-cells covered with?

  Antibodies
• what are antibodies?

  proteins that bind antigens to form an antigen-antibody complex
• what does each B-cell have?

  a different shaped antibody on its membrane, so different ones bind to different shaped antigens
• how do B-cells work?


  1. When the antibody on the surface of a B-cell meets a complementary shaped antigen, it binds to it
  2. This, together with substances released from helper T-cells, activates the B-cell. This process is called CLONAL SELECTION
  3. The activated B-cell divides into plasma cells
• what do B-cells divide into?

  plasma cells and memory cells
• What are plasma cells identical to?

  the B-cell (they're CLONES)
• What do plasma cells do?


  secrete lots of antibodies specific to the antigen

  these are called monoclonal antibodies
• what do the monoclonal antibodies secreted by plasma cells do?


  they bind to the antigens on the surface of the pathogen to form lots of antigen-antibody complexes
• what does an antibody have?


  • 2 binding sites , so can bind to two pathogens at the same time
  • This means that pathogens become clumped together - this is called AGGLUTINATION
  • Phagocytes then bind to the antibodies and phagocytose MANY pathogens at once
  • This process leads to the destruction of pathogens carrying this antigen in the body
• what type of molecule are antibodies?

  proteins