Biology - AQA - Unit 2 - C5. Antibodies in Medicine

Monoclonal antibodies are antibodies produced from a single group of genetically identical B-cells (plasma cells). This means that they’re all identical in structure.
Antibodies are very specific because their binding sites have a unique tertiary structure that only an antigen with a complementary shape can fit into. You can make monoclonal antibodies that bind to anything 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 illnesses and in medical diagnosis.

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.

Pregnancy tests detect the hormone human chorionic gonadotropin (hCG)
that’s found in the urine of pregnant women: The application area contains antibodies that are complementary to the hCG protein, 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 any hCG-concentrating the hCG-antibody complex with the blue beads attached. If no hCG is present, the beads will pass through the test area without binding to anything, and so it won’t go blue.

A direct ELISA uses a single antibody that is complementary to the antigen you’re testing for.

1) Antigens from a patient sample are bound to the inside of a well in a well plate.

2) A detection antibody (with an attached enzyme) that is complementary to the antigen of interest is added.

3) If the antigen of interest is present in the patient sample, it will be immobilised on the inside surface of the well and the detection antibody will bind to it.

4) The well is then washed out to remove any unbound antibody and a substrate solution is added.

5) If the detection antibody is present, the enzyme reacts with the substrate to give a colour change. This is a positive result for presence of the antigen.

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

2. A sample of the patient’s blood plasma, which might contain several different antibodies, is added to the well. If there are any HIV-specific antibodies in the plasma (i.e. antibodies against HIV) 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.

3. A secondary antibody, that has a specific enzyme attached to it, is added to the well. This secondary antibody can bind to the HIV-specific antibody (which is also called the primary antibody). The well is washed out again to remove any unbound secondary antibody. If there’s no primary antibody in the sample, all of the secondary antibody will be washed away because there will be nothing for it to bind to.

4. A solution is added to the well. This 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 and is infected with HIV.

Ethical issues surrounding monoclonal antibody therapy often involve animal rights issues. 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.