Monoclonal antibodies

When a pathogen invades the body, it displays many different antigens on its surface, which leads to the activation of a variety of B cells and the production of numerous types of antibodies. Sometimes, scientists need a pure sample of a single type of antibody, produced by one type of plasma cell, that is specific to a single antigen—these are known as monoclonal antibodies.

Monoclonal antibodies are utilised for a number of functions in medical science, including targetting medication, medical diagnosis using ELISA tests, and pregnancy tests.

Targeting medication

Monoclonal antibodies can be designed to target drugs to specific cells, such as cancer cells:

1. Antibodies are produced to be specific to an antigen, or tumour marker, on cancer cells.

2. An anticancer drug is then attached to the constant (Fc) region of the antibody.

3. When administered, these antibodies bind to the tumour markers on cancer cells, delivering the drug directly to the cancer cells.

4. This focused delivery reduces side effects, as the drug predominantly affects cancer cells and spares healthy cells.

Alternatively, monoclonal antibodies can be made to bind to cancer cell surfaces, disrupting signalling mechanisms that the cancer cells need to grow and divide, effectively slowing down or stopping tumour growth.

Medical diagnosis using ELISA tests

The ELISA (Enzyme-Linked Immunosorbent Assay) test uses monoclonal antibodies to detect specific antigens in a sample, such as the HIV virus in blood.

In an ELISA test:

• An enzyme is attached to the constant (Fc) region of a monoclonal antibody.

• The variable (Fab) region of this antibody is specific to the constant region of the target antibody or antigen.

• The enzyme catalyses a reaction that converts a colorless substrate into a coloured product, indicating the presence of the antigen.

The steps for an indirect ELISA test for HIV are as follows:

1. A known HIV antigen is attached to the bottom of a well on a plate.

2. The well is washed to remove any unattached antigens.

3. A sample from the person being tested is added; if HIV-specific antibodies are present, they bind to the antigens.

4. The surface is washed to remove any unbound antibodies.

5. A secondary antibody, which binds to the primary antibody and has an enzyme attached, is added.

6. The surface is washed again to remove excess secondary antibody.

7. A colorless substrate of the enzyme is added, which the enzyme converts into a coloured product if the primary antibody is present.

8. The intensity of the colour is directly proportional to the concentration of HIV-specific antibodies in the sample. Any colour formation generally indicates HIV infection.

Diagnosis of HIV infection using monoclonal antibodies.

Pregnancy tests

Home pregnancy test kits enable early detection of pregnancy.

The placenta of a pregnant woman produces the hormone human chorionic gonadotropin (hCG), which is excreted in urine.

The test strip contains monoclonal antibodies linked to coloured beads. If hCG is present in the urine, it binds to these antibodies, forming an hCG-antibody-colour complex.

This complex moves along the test strip until it is trapped by another monoclonal antibody specific to hCG, forming a coloured line on the test strip. If hCG is not present, no colour will appear on the test strip.

Ethical concerns

The use of monoclonal antibodies raises ethical concerns, including issues related to animal testing (since animals are often used to produce the initial antibodies) and potential side effects in humans. Additionally, some people have ethical or religious objections to the techniques used in their development and application.

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