antibodies and antibodies in medicine

what are 2 uses of monoclonal antibodies?

• targeted medication

• medical diagnosis

targeted medication?

• cancer cells in the body have antigens that signal the cells as abnormal

• monoclonal antibodies in cancer treatment can be used to bind specifically to the antigens on cancer cells

• cancer treatments can be harmful to many cells; by binding specifically to cancer cells, the antibodies allow the treatment to be targeted only to cancer cells

• this reduces damage to other cells

monoclonal antibodies example: targeting drugs to specific cell type (cancer)

• different cells in the body have different surface antigens

• cancer cells have antigens called tumour markers that are 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

medical diagnosis?

• monoclonal antibodies can be used to indicate the presence of a specific antigen

• the antibodies are attached to a dye, fluorescent or radioactive marker

• when the complementary antigen is present, it will bind the antibody and the marker will become visible

• monoclonal antibodies are used in this way in pregnancy test

monoclonal antibodies example: targeting a specific substance for medical diagnosis (pregnancy testing)

(pregnancy tests detect the hormone hCG which is found in the urine of a pregnant woman

• the application area contains antibodies for hCG bound to a coloured bead (blue)

• when urine is applied to the application area, any hCG will bind to the antibody on the beads, forming an antigen-antibody complex

• the urine moves up the stick to the test strip, carrying any beads with it

• the test strip contains antibodies to hCG that are stuck in place (immobilised)

• if there is hCG present, the test strip turns blue because the immobilised antibody binds to hCG

• if there is no hCG present, the beads will pass through the test area without binding to anything, and so it won’t go blue

what test can antibodies be used in?

• the ELISA test

what is the ELISA test?

• it tests for infections such as HIV or allergies

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

overall summary of the 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 vessel to change colour

• if there’s a colour change, it shows that the antigen or antibody of interest is present in the sample being tested

  • in some types of ELISA, the quantity of this antigen/antibody can be worked out from the intensity of the colour change

example: using ELISA as a HIV test?

• HIV antigen is bound to the bottom of a well in a well plate

• a sample of the patient’s blood plasma, which may contain several antibodies is added to the well.

  • if there are any HIV specific antibodies, these will bind to the HIV antigen stuck to the bottom of the well.

• the well is then washed out to remove any unbound antibodies

• a secondary antibody, that has a specific enzyme attached to it, is added to the well

  • the secondary antibody can bind to the HIV specific antibody (also called the primary antibody)

• the well is washed out again to remove any unbound secondary antibody. if there is no primary antibody in the sample, all of the secondary antibody will be washed away

• a solution is added to the well. the solution contains a substrate, which is able to react with the enzyme attached to the secondary antibody and produce a coloured product.

  • if the solution changes colour, it indicates that the patient has HIV-specific antibodies in their blood (as it means that the secondary antibodies have bound to the antibodies in the blood sample) and is infected with HIV.

antibody structure?

• an antibody has 2 binding sites, so can bind to 2 pathogens at the same time

• this means that the pathogens become clumped together - agglutination

• phagocytes can 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 are antibodies made from?

• 2 heavy chains and 2 light chains

• the heavy chains are connected to the light chains by disulphide bridges

what does the specificity of the antibody depend on?

• the variable regions, which form the antigen binding sites

• each antibody has a variable regions with a unique tertiary structure (due to different amino acid sequences) that’s complementary to one specific antigen

• all antibodies have the same constant region

  • the hinge protein connects the variable region to the constant region

ethical issues surrounding vaccines: animal testing?

• all vaccines are tested on animals before tested on humans, some people disagree with animal testing.

  • also, animal based substances may be used to produce a vaccine, which some people disagree with

ethical issues surrounding vaccines: testing on humans?

• testing vaccines on humans can be tricky

  • e.g- volunteers putting themselves at unnecessary risk of contracting the disease because they think they are fully protected

    • e.g- they might have unprotected sex because they have had a new HIV vaccine and think they are protected, and the vaccine may not work

ethical issues surrounding vaccines: personal?

• some people don’t want to take the vaccine due to risk of side effects, but they are still protected because of herd immunity

  • other people think this is unfair

ethical issues surrounding vaccines: vaccine priority?

• if there was an epidemic of a new disease, there would be a rush to receive a vaccine and difficult decisions would have to be made about who would be the first to receive it

what are monoclonal antibodies made from?

• animals produce the cells from which the monoclonal antibodies are produced

• some people disagree with this use of animals in this way, which is why there are animal rights issues regarding this