What is a monoclonal antibody?
Your white blood cells called lymphocytes make antibodies. An antibody is a Y-shaped protein.
Each antibody fits only one antigen. An antigen is a special shape (a protein) on the surface of a cell or a germ.
Monoclonal means "from one clone". A clone is a group of cells that are all exact copies. So monoclonal antibodies are many identical antibodies that all stick to the same one antigen.
Because they target one thing only, we call them specific.
Producing monoclonal antibodies
- A mouse is injected with the chosen antigen.
- The mouse makes lymphocytes that produce the matching antibody. These lymphocytes are collected.
- Lymphocytes do not divide well on their own. So each one is fused with a tumour cell (a myeloma cell), which divides fast and without stopping.
- The fused cell is called a hybridoma. It makes the antibody AND keeps dividing.
- A single hybridoma is chosen and cloned. The clone makes huge amounts of identical antibody.
- The antibodies are collected and purified.
Hybridoma = hybrid (mixed) + -oma (tumour).
Uses of monoclonal antibodies
1. Pregnancy tests
A pregnant woman's urine contains the hormone hCG. Antibodies on the test strip catch hCG. Coloured beads joined to the antibodies collect on a line, so a coloured line shows a positive result. A control line shows the test worked.
2. Lab and hospital tests
They measure the amount of hormones and other chemicals in blood, and they detect pathogens (germs).
3. Research: finding molecules
An antibody joined to a fluorescent dye sticks to one molecule. Scientists then see exactly where it is in a cell or tissue, for example a blood clot or cancer cells.
4. Treating diseases such as cancer
An antibody can carry a radioactive substance, a toxic drug or a chemical that stops cell growth straight to cancer cells. Some simply mark cancer cells so the immune system destroys them.
Advantages and disadvantages
Advantages: they bind only to their target, so healthy cells are mostly not harmed; they can be made for many different antigens; tests using them are quick and accurate.
Disadvantages: some treatments caused more side effects than expected (for example fever, sickness, rashes, low blood pressure); they are expensive to make; using mice raises ethical questions for some people.
Exam tip: questions often ask you to evaluate their use. Give a benefit, a drawback, then a conclusion.
Key formulas and definitions
- Antibody: a Y-shaped protein made by lymphocytes that binds to one specific antigen
- Antigen: a protein shape on a cell or pathogen that an antibody recognises
- Hybridoma = lymphocyte (makes antibody) + tumour cell (divides fast)
- Monoclonal = all antibodies come from one clone and are identical
- hCG: the pregnancy hormone detected by pregnancy test strips
Worked examples
1. Why is a lymphocyte fused with a tumour cell, instead of just growing lymphocytes?
Lymphocytes make the right antibody but do not divide well outside the body. Tumour cells divide quickly and endlessly but make no useful antibody. The hybridoma has both features, so it can be cloned into many cells that all make the antibody.
2. A pregnancy test shows a line in the control window only. What does it mean?
The control line shows the test worked. No line in the result window means no hCG was caught, so the result is negative (not pregnant). If even the control line is missing, the test failed.
3. Why can a monoclonal antibody drug for cancer cause fewer harmful effects than ordinary chemotherapy?
Ordinary chemotherapy affects all fast-dividing cells, including healthy ones. The antibody binds only to the antigen on cancer cells, so the attached drug reaches mainly cancer cells and fewer healthy cells are damaged.
Common mistakes
- Saying the mouse itself makes monoclonal antibodies for us. The mouse only gives the lymphocytes; the antibodies are made by hybridoma clones in the lab.
- Mixing up antigen and antibody. The antigen is the shape on the cell or germ; the antibody is the Y-shaped protein that sticks to it.
- Thinking monoclonal antibodies kill germs like antibiotics. They bind to a target; killing happens through an attached drug or the immune system.
- Saying they have no side effects. Early treatments caused more side effects than expected.