Antibodies in Medicine

• monoclonal antibodies are antibodies produced from a single group of genetically identical B-cells (plasma cells) - means they are all identical in structure
• Antibodies are very specific bc their binding sites have a unique tertiary structure that only an antigen with a complementary shape can fit into.
• You can make monoclonal antibodies bind to whatever you want e.g. a cell antigen or other substance, and they will only bind to (target) this molecule. This can be useful for both treating illness and in medical diagnosis
• Anti-cancer drugs targeted to cancer cells:

  different cells in the body have different surface antigens

  cancer cells have antigens called tumour markers not found on normal body cells

  monoclonal antibodies can be made that will bind to the tumour markers

  you can also attach anti-cancer drugs to the antibodies
• When the antibodies come into contact with the cancer cells they will bind to the tumour markers

  this means the drug will only accumulate in the body where there are cancer cells

  so the side effects of an antibody-based drug are lower than other drugs because they accumulate near specific cells
• pregnancy tests detect the hormone human chorionic gonadotropin (hCG) that is found in the urine of pregnant women
• How pregnancy tests work

  1. Application area contains antibodies complementary to hCG protein bound to blue coloured bead

  2. Urine applied to application area, any hCG binds to antibody on beads forming antigen-antibody complex

  3. Urine moves up stick to test strip, carrying any beads with it

  4. Test strip contains antibodies to hCG stuck in place (immobilised)

  5. If hCG present, test strip turns blue as immobilised antibody binds to hCG - concentrating hCG-antibody complex with blue beads

  6. If no hCG present, beads pass through test area without binding to anything, so no blue colour
• ELISA test = the enzyme-linked immunosorbent assay

  allows you to see if a patient has any antibodies to a certain antigen or any antigen to a certain antibody

  can be used in medical diagnosis
• The ELISA test can be used in medical diagnosis to test for pathogenic infections (e.g. HIV infection), for allergies and pretty much anything you can make an antibody for
• In an ELISA test, an antibody is used which has an enzyme attached to it. This enzyme can react with a substrate to produce a coloured product

  this causes the solution in the reaction vessel to change colour
• If there is a colour change - demonstrates that the antigen or antibody of interest is present in the sample being tested (e.g. blood plasma).

  In some types of ELISA - quantity of this antigen/ antibody can be worked out from the intensity of the colour change
• Direct ELISA - uses a single antibody that is complementary to the antigen you are testing for
• 1. antigens from patient sample bound to inside of a well in a well plate
  2. detection antibody (with attached enzyme) that is complementary to antigen of interest is added
  3. if antigen of interest present in patient sample, it will be immobilised on inside surface of well and detection antibody will bind to it
  4. well is washed out to remove any unbound antibody and substrate solution is added
  5. if detection antibody is present, enzyme reacts with substrate to give colour change
  6. positive result for presence of antigen
• Indirect ELISA: uses two different antibodies
• Indirect ELISA test to detect HIV antibodies

  1. HIV antigen bound to bottom of a well in well plate

  2. Sample of patient's blood plasma, which might contain several different antibodies added to the well

  3. If there are any HIV specific antibodies in the plasma these will bind to the HIV antigen stuck to bottom of the well

  4. Well is washed out to remove any unbound antibodies

  5. Secondary antibody that has a specific enzyme attached is added to the well - this can bind to the HIV specific antibody (primary antibody)

  6. Well washed out again to remove any unbound secondary antibody

  7. Solution added to the well - contains a substrate which is able to react with the enzyme attached to secondary antibody and produce a coloured product
• If solution changes colour

  Indicates they have HIV-specific antibodies in blood - infected with HIV
• If negative - no colour change as there would be no HIV-specific antibodies for secondary antibodies to bind to
• Ethical issues - animal rights

  animals are used to produce the cells from which the monoclonal antibodies are produced

  some people disagree with the use of animals in this way