Cells (Immunity) - Antibodies Flashcards
What are antibodies?
Antibodies are glycoproteins with specific binding sites synthesised by B cells. When the body is infected by non-self material, a B cell produces a specific antibody. This specific antibody reacts with an antigen on the surface of the non-self material by binding to them, forming an antigen-antibody complex. Each antibody has two identical sites. The antibody binding sites are complementary to a specific antigen. The massive variety of antibodies is possible because they are made of proteins.
What is the structure of antibodies?
Antibodies are Y shaped and are made up of four polypeptide chains. The chains of one pair are long and are called heavy chains, while the chains of the other pair are shorter and are known as light chains.
Each antibody has a specific binding site that fits very precisely onto a specific antigen to form what is known as an antigen-antibody complex. The binding site is different on different antibodies and is therefore called the variable region. Each antibody has two variable regions. Each binding site consists of a sequence of amino acids that form a specific 3D shape that binds directly to a specific antigen.
The rest of the antibody is known as the constant region. Every antibody has the same constant region. This binds to receptors on cells such as B cells and phagocytes.
Antibodies have flexible hinge regions, making them more flexible, so can bind to multiple antigens.
How do antibodies lead to the destruction of antigens?
Antibodies do not destroy antigens directly but rather prepare the antigen for destruction. Different antibodies lead to the destruction of an antigen in a range of ways.
How do antibodies assist in the destruction when the antigen is a bacterial cell?
- They cause agglutination of the bacterial cells. In this way clumps of bacterial cells are formed, making it easier for the phagocytes to locate them as they are less spread-out within the body.
- They then serve as markers that stimulate phagocytes to engulf the bacterial cells to which they are attached.
Why is agglutination possible?
Because each antibody has two antigen binding sites.
What are monoclonal antibodies?
A bacterium or other microorganism entering the body is likely to have many hundreds of different antigens on its surface. Each antigen will induce a different B cell to multiply and form a clone of itself. Each of these clones will produce a different antibody. It is of considerable medical value to be able to produce antibodies outside the body. It is even better if a single type of antibody can be isolated and cloned. Such antibodies are known as monoclonal antibodies.
Monoclonal antibodies have a number of useful functions in science and medicine.
How can monoclonal antibodies be used to target medication to specific cell types?
As an antibody is very specific to particular antigen (protein), monoclonal antibodies can be used to target specific substances and specific cells. One type of cell they can target is cancer cells. Monoclonal antibodies can be used to treat cancer in a number of ways.
What is direct monoclonal antibody therapy?
- Monoclonal antibodies are produced that are specific to antigens on cancer cells.
- These antibodies are given to a patient and attach themselves to the receptors on their cancer cells.
- They attach to the surface of their cancer cells and block the chemical signals that stimulate their uncontrolled growth.
What is the advantage of direct monoclonal antibody therapy?
The advantage of direct monoclonal antibody therapy is that since the antibodies are not toxic and are highly specific, they lead to fewer side effects than other forms of therapy.
What is indirect monoclonal antibody therapy?
Indirect monoclonal antibody therapy involves attaching a radioactive or cytotoxic drug (a drug that kills cells) to the monoclonal antibody. When the antibody attaches to the cancer cells, it kills them.
What is the advantage of indirect monoclonal antibody therapy?
They are referred to as ‘magic bullets’ and can be used in smaller doses, as they are targeted on specific sites. Using them in smaller doses is not only cheaper, but also reduces any side effect the drug might have.
How are monoclonal antibodies used in medical diagnosis?
Monoclonal antibodies are an invaluable tool in diagnosing disease with over a hundred different diagnostic products based on them. They are used for the diagnosis of influenza, hepatitis and chlamydia infections where they produce a much more rapid result than conventional methods of diagnosis. They are important in diagnosing certain cancers.
In medical diagnosis, they can be used to detect particular antigens in patient samples of blood or tissue.
How can monoclonal antibodies be used in diagnosing prostate cancer?
Men with prostate cancer often produce more of a protein called prostate specific antigen (PSA) leading to unusually high levels of it in the blood. By using a monoclonal antibody that interacts with this antigen, it is possible to obtain a measure of the level of PSA in a sample of blood. While a higher normal level of PSA is not itself diagnostic of the disease, it gives an early warning of its possibility and the need for further tests.
How are monoclonal antibodies used in pregnancy testing?
It is important that a mother knows as early as possible that she is pregnant, not least because there are certain actions she can take to ensure the welfare of herself and her unborn baby. The use of pregnancy testing kits that can easily be used at home has made possible the early detection of a pregnancy.
These kits rely on the fact that the placenta produces a hormone called hCG and that this is found in the mother’s urine. Monoclonal antibodies present on the test strip of a home pregnancy testing kit are linked to coloured particles. If hCG is present in the urine, it binds to these antibodies. The hCG-antibody-colour complex moves along the strip until it is trapped by a different type of antibody creating a coloured line.
What are the ethical issues associated with the use of monoclonal antibodies?
- Production of monoclonal antibodies involves the use of mice. These mice are used to produce both antibodies and tumour cells. The production of tumour cells involves deliberately inducing cancer in mice. Despite the specific guidelines drawn up to minimise any suffering, some people still have reservations about using animals in this way.
- Monoclonal antibodies have been used successfully to treat a number of diseases, including cancer and diabetes, saving many lives. There have also been some deaths associated with their use in the treatment of multiple sclerosis. It is important that patients have full knowledge of the risks and benefits of these drugs before giving permission for them to be used (=informed consent).
- Testing for the safety of new drugs presents certain dangers. In March 2006, six healthy volunteers took part in the trial of a new monoclonal antibody in London. Within minutes, they suffered multiple organ failure, probably as a result of T cells overproducing chemicals that stimulate an immune response or attaching the body tissues. All the volunteers survived, but it raises issues about the conduct of drug trials.
