The immune system

• antigens are molecules that can generate an immune response when detected.

  • They are usually found on the surface of a cell & are used by the immune system to identify; pathogens, abnormal body cells & toxins.
• what are the 4 main stages of the immune response?

  1. phagocyte engulfs pathogen.
  2. Phagocyte activates T-cells.
  3. T-cells activate B-cells.
  4. Plasma cells produce antibodies to a specific antigen.
• a phagocyte is a type of white blood cells that carries out phagocytosis
• immune response 1:

  • a phagocyte recognises the foreign antigens on a pathogen.
  • the phagocyte engulfs the pathogen forming a phagocytic vacuole.
  • a lysosome containing hydrolytic enzymes fuses with the phagocytic vacuole & breaks down the pathogen inside.
  • the phagocyte then presents the pathogens antigens on its surface becoming an antigen-presenting-cell.
• immune response 2:

  • a T-cell has specific receptor proteins on its surface that can bind to complementary antigens presented by the phagocyte.
  • This stimulates other T-cells.
  • Helper T-cells are stimulated to activate more phagocytes and stimulate cytotoxic T-cells.
  • Helper T-cells also activate B-cells which secrete antibodies.
• T-cells / T-lymphocytes are another type of white blood cell
• the role of cytotoxic T-cells is to kill abnormal & foreign cells.
• which cells do T-cells stimulate?

  • B-cells
  • Phagocytes
  • Cytotoxic t-cells
• B-cells / B-lymphocytes are a type of white blood cell that produce antibodies.
• immune response 3:

  • When an antibody of a B-cells meets with a complementary shaped antigen they bind together.
  • forming an antibody-antigen complex.
  • this stimulates the B-cell to divide into plasma cells.
  • this is called clonal selection.
• plasma cells are identical to B-cells (clones), they secrete specific antibodies to an antigen.

  • these are called monoclonal antibodies.
• monoclonal antibodies bind to antigens on the surface of pathogens to form many antigen-antibody complexes.
• antibodies are proteins.

  • they are made up of chains of amino acids.
  • the specificity of the antibody depends on the variable regions which form the antigen binding sites.
  • each antibody has a specific tertiary structure thats complementary to one specific antigen.
• immune response 4:

  • plasma cells produce & secrete specific antibodies which bind to the antigens on pathogens.
  • they have two binding sites so can bind with two pathogens at a time.
  • this causes pathogens to be clumped together by agglutination.
  • phagocytes then bind to the antibodies and complete phagocytosis.
• cellular immune system = the T-cells, phagocytes & other immune cells they interact with.
• the humoral response = B-cells, clonal selection & production of monoclonal antibodies.
• what are the two types of immune response?

  clonal & humoral
• the primary immune response:

  • when an antigen enters the body for the first time.
  • the primary response is slower because there aren't many B-cells that make the specific antibody to the antigen.
  • after exposure both T-cells & B-cells will produce memory cells.
  • Memory T-cells remember specific antigens.
  • Memory B-cells remember specific antibodies for the antigen.
  • The person is now immune & can respond quickly to secondary infection.
• the secondary immune response:

  • if the same pathogen enters the body again the immune response is quicker & stronger.
  • Clonal selection occurs faster as memory B-cells are activated & divide into plasma cells that secrete a specific antibody.
  • Memory T-cells are activated to divide into a specific T-cells to kill the antigen carrying cell (pathogen).
  • the secondary response usually gets rid of the pathogen before symptoms show.
• vaccines contain antigens that cause the body to produce memory cells against a specific pathogen, without causing disease.
• vaccines provide herd immunity
• a disadvantage of taking vaccines orally is they may be digested by enzymes in the gut.
• antigens on the surface of pathogens stimulate a primary response.
• antigenic variability is when pathogens change the antigens on their surface so memory cells will not recognise them causing a primary response instead.
• immunity can be active or passive
• active immunity is when the immune system makes its own antibodies after being stimulated by an antigen.
• there are two types of active immunity:

  • natural
  • artificial
• what is an example of natural active immunity?

  when you become immune after catching the disease & produce your own antibodies
• what is an example of artificial active immunity?

  when you become immune after being given a vaccination containing a harmless antigen, you still make your own antibodies just no symptoms occur.
• passive immunity is the body is given antibodies made by a different organism - your immune system does not produce any antibodies of its own.
• what are the two types of passive immunity?

  • natural
  • artificial
• what is an example of natural passive immunity?

  when a baby becomes immune due to antibodies received from breast milk.
• what is an example of artificial passive immunity?

  when you become immune after beinng injected with antibodies from someone else.
• active immunity:

  • requires exposure to the antigen.
  • take a while for antibodes to develop
  • memory cells are produced
  • provides long term immunity
• passive immunity:

  • does not require exposure to the antigen
  • response is immediate
  • memory cells are not produced
  • provides short term protection
• monoclonal antibodies are produced from a single group of genetically identical B-cells / plasma cells
• antibodies are very specific because their binding sites have a unique tertiary structure that only one specific antigen can bind to.
• pregnancy tests:

  • the application area contains antibodies for hCG bound with a blue coloured bead.
  • when urine is applies to the application area, any hCG will bind to the antibody on the beads, forming an antigen-antibody complex.
  • the urine moves up the test strip carrying any beads with it.
  • the test strip contains immobilised antibodies to hCG.
  • if there is hCG present the immobilised antibody will bind with the hCG thats also got the antibody with the bead on it.
  • turning the test strip blue due to the coloured bead.
• the ELISA test allows you to see if a patirnt has any antibodies to an antigen or any antigens to a certain antibody.
• ELISA tests can be used to test for pathogenic infections , allergies, ect