Monoclonal Antibodies Bind to One Specific Target

1. A monoclonal antibody binds to one binding site on one antigen.
2. That antigen may be on a specific type of cell, or it may be a specific chemical such as a hormone.
3. Because they are so specific, they can find, measure or treat one target without affecting other cells.
4. A marker, such as a fluorescent dye or a radioactive label, can be attached so the antibody can be tracked.

Pregnancy Tests Detect a Hormone in Urine

1. A pregnancy test uses monoclonal antibodies that bind to the hormone HCG (human chorionic gonadotropin), which is made in early pregnancy and passed out in the urine.
2. If HCG is present, the antibodies bind to it and produce a colour change, giving a positive result.
3. If HCG is absent, the antibodies have nothing to bind to and no line appears.

Diagnosis, Measuring and Research

1. Diagnosis
   1. Antibodies are made to bind to antigens on pathogens, blood clots or cancer cells; a marker shows doctors where they build up, so problems can be found early, as in the blood test for prostate cancer.
2. Measuring and monitoring
   1. In laboratories they measure the level of a hormone or other chemical in the blood, or detect a pathogen, such as screening donated blood for HIV.
3. Research
   1. Antibodies attached to a fluorescent dye bind to specific molecules in a cell or tissue, so scientists can see where those molecules are.

Treating Cancer With a Targeted Antibody

1. Monoclonal antibodies can be made to bind to antigens on cancer cells.
2. The antibody can carry a radioactive substance, a toxic drug, or a chemical that stops cells growing and dividing.
3. Because it binds only to the cancer cells, it delivers the substance straight to them without harming healthy cells.
4. A monoclonal antibody can also block receptors on a cancer cell so it stops growing, or trigger the immune system to attack it.

Weighing Up Monoclonal Antibodies

1. Advantages
   1. They are very specific, so they treat or detect one target without affecting healthy cells.
   2. They can be produced against a huge range of antigens, so they could be used to treat many different conditions.
2. Disadvantages
   1. They created more side effects than expected, partly because early ones used mouse cells that triggered an immune response in humans.
   2. They are expensive and difficult to produce, so they are not yet as widely used as everyone first hoped.