Antibodies and vaccination

Active and passive immunisations are effective ways to treat and prevent infectious diseases. Smallpox has been eradicated; other diseases may soon follow, but vaccine development has proved more difficult for diseases such as malaria.

1. Relate the molecular structure of antibodies to their functions

• An antibody is made by B cells
• An antibody consists of four polypeptide chains; two 'long' or 'heavy' chains and two 'short' and 'light' chains so it is a globular glycoprotein with a quarternary structure
• Disulfide bonds hold the chains together
• Each molecule has two identical antigen binding sites, which are formed by both light and heavy chains
• The amino acid sequences in these regions make the specific 3D shape which binds to just one type of antigen
• The antigen-binding sites form the variable region which makes each antibody different from one another
• The 'hinge' region gives the antibody its flexibility for it to bind around the antigen

2. Outline the hybridoma method for the production of monoclonal antibodies

• Monoclonal antibodies (Mabs) are produced by cell fusion
• A small number of plasma cells producing a particular type of antibody were fused with cancer cells
• E.g. These types of B cells need to fuse with malignant B myeloma cells (cancerous B cells)
• This is because cancer cells go on dividing indefinitely
• The cell produced by this fusion of a plasma cell and a cancerous cell is called a hybridoma
• The hybridoma cells divide by mitosis and secrete antibodies which are specific antibodies that were originally produced by the clone of B cells
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3. Outline the use of monoclonal antibodies in the diagnosis of disease and in the treatment of disease

a) Monoclonal antibodies in diagnosis

• Mabs can be used to locate the position of blood clots in the body of a person thought to have deep vein thrombosis
  • Antibodies are produced by injecting a mouse with human fibrin
  • The mouse makes many plasma cells that secrete antibody against fibrin
  • These plasma cells are collected from the spleen and fused with cancer cells to form hydridomas that secrete fibrin antibodies
• Detection of HIV/AIDS by the ELISA test
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• Distinguishing between different types of leukaemias
• Pregnancy tests
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• Mabs can be used to locate cancer cells which have proteins in their cell surface membranes that differe from proteins on a normal body cell and can therefore be detected by antibodies
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• Mabs can also be used to identify the exact strain of virus or bacterium that is causing an infection and this speeds up the choice of the most appropriate treatment
• Mabs is used routinely in blood typing before transfusion
• And tissue typing before transplants

b) Monoclonal antibodies in treatment

• Mabs need to be administered more than once when used as treatment which presents problems
• The antibodies are produced by lab animals such as rabbits and mice
• When introduced into humans, they trigger an immune response because they are foreign antigens
• This problem is overcome by humanising Mabs
  • altering the genes that code for the polypeptide chains of the antibodies so that they code for human sequences of amino acids
  • changing the…