• Monoclonal antibodies are identical antibodies with the same tertiary structure, produced by clones of a single B-lymphocyte.
• They are designed to bind to one specific antigen, their antigen binding sites will be complementary to the same antigen.

Medical Diagnosis

• Monoclonal antibodies are used in diagnosis. They are used to produce kits to diagnose diseases and are very quick and reliable.

Examples:

• Testing for prostate cancer in men. Blood serum is tested for prostate specific antigen (PSA). If PSA is found in a high concentration this is a potential sign of prostate cancer and further tests are carried out.
• They can also be used in pregnancy tests to detect hCG hormone in a female's urine.
• They can be used to diagnose a HIV infection.

Treatment of Diseases

• Cancer therapy.
• 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.
• Anti-cancer drugs (eg. radioactive substances) can also be attached to the monoclonal antibodies.
• This is then injected into the patient. When antibodies come into contact with the cancer cells they will bind to the tumour markers.
• This results in the drug accumulating in the body where there are cancer cells.
• Therefore, the side effects of an antibody-based drug are lower than other drugs because they accumulate near cancer cells only. They don’t damage normal body cells.

• ELISA is used to detect the presence and concentration of antigens or antibodies in a sample.
• It relies on antigen-antibody interactions and an enzyme-linked reaction to produce a colour change, indicating a positive result.

Types of ELISA Tests

Antigen Detection

• Detects a specific antigen in a patient's sample (e.g., blood serum).
• Steps:

1. 1. Coat the well plate with the first Antibody: This binds to the target antigen.
   2. Add the Sample: If the antigen is present, it binds to the first antibody.
   3. Add an Enzyme-Linked Secondary Antibody: This binds to the antigen if present.
   4. Wash off Unbound Antibodies: Prevents false positives that would be caused by any unbound second antibodies still remaining.
   5. Add a Substrate: If the enzyme is present (i.e., antigen was captured) the substrate is broken down and a colour change occurs.
   6. Measure Absorbance: The more antigen present, the more intense the colour. This indicates a higher concentration of the antigen in the sample.

The diagram shows an example where PSA (prostate specific antigen) is being tested for in a blood sample. This antigen can indicate prostate cancer.

Antibody Detection

• Detects specific antibodies in a patient’s sample (e.g., blood serum). Useful for detecting viral infections that may be inside host cells,so antigens would not be exposed.
• Steps:

1. 1. Coat the well plate with a known antigen (e.g., HIV surface proteins).
   2. Add the sample: If antibodies are present, they will bind to the antigen.
   3. Wash off any unbound antibodies: Any antibodies not specific to the target antigen will be removed.
   4. Add an enzyme-linked secondary antibody: That binds to HIV antibodies if present.
   5. Wash off unbound secondary antibodies to prevent false positives.
   6. Add a substrate: If the patient has antibodies against the antigen, the substrate is broken down and a colour change occurs.
   7. Measure absorbance: To determine antibody levels. The more antibodies present, the more intense the colour. This indicates a higher concentration of the antibody in the sample.

The diagram shows an example where HIV antibodies are being tested for in a blood sample. The presence of HIV antibodies would indicate infection with HIV.