Antibodies

• • Antibodies are proteins with specific binding sites synthesised by B cells. When the body is infected by non-self material, a B cell produces a specific antibody.
• • Each specific antibody has two identical binding sites, the antibody binding sites are complementary to a specific antigen. Forming an antigen-antibody complex
  • The binding site is different on different antibodies so is called a variable region.
  • Each binding site consists of a sequence of amino acids that form a specific 3D shape that binds directly to a specific antigen
  • Rest of antibody = constant region, this binds to receptors on cells like B cells.
• Antigen - antibody complex

  A) variable regions

  B) constant regions

  C) disulphide bridge

  D) heavy chain

  E) light chain

  F) antigen

  
• How the antibody leads to the destruction of antigen. 

  • Does Not destroy antigens directly but prepares the antigen for destruction
  • They cause agglutination of the bacterial cells, in this way clumps of bacteria cells are formed, making it easier for the phagocytes to locate them as they are less spread out in the body.
  • Serve as markers that stimulate phagocytes to engulf the bacterial cells to which they are attached.
• Monoclonal antibodies:

  • Each antigen will induce a different B cell to multiply and form a clone of itself, each of these clones produces a different antibody.
  • Medical value to produce antibodies outside the body, even better if a SINGLE type of antibody can be isolated and cloned = monoclonal antibodies
• • As an antibody is very specific to an antigen, monoclonal antibodies can be used to target specific substances and cells. 
  • One cell they can target is cancer cells, monoclonal antibodies can be used to treat cancer in a number of ways
• Monoclonal antibodies treating cancer cells.

  1. Monoclonal antibodies are produced that are specific to antigens on cancer cells
  2. These antibodies are given to patients and attach themselves to receptors on cancer cells.
  3. They attack to the surface of cancer cells and block the chemical signals that stimulate uncontrolled growth
  4. E.g herceptin, monoclonal antibody therapy involving attaching radioactive or cytotoxic drug to the monoclonal antibody, when antibody attaches to cancer cells it kills them
• • Using monoclonal antibodies in small doses is cheaper and reduces side effects.
• Monoclonal antibodies: Medical diagnosis:

  • Used for diagnosis of influenza, hepatitis and chlamydia, producing a more rapid result than other diagnosis techniques.
  • Important diagnosing certain cancers, men with prostate cancer often produce more of a protein called prostate specific antigen leading to 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 level of PSA in a sample blood.
  • Higher than normal level of PSA gives an early warning of possibility and need for further tests.
• Monoclonal antibodies: pregnancy tests

  Home pregnancy test kits rely on the idea that placenta produces a hormone called ( hCG) which is found in the women's urine. Monoclonal antibodies present in 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 trapped by a different type of antibody creating a coloured line.
• Ethical use of monoclonal antibodies:

  • Deaths associated with treatment of multiple sclerosis, important patients have full knowledge of the risks and benefits of these drugs before giving permission.
  • March 2006, healthy volunteers took part in a trial of a new monoclonal antibody and suffered from organ failure, which could be due to T cells overproducing chemicals that stimulate an immune response or attacking body tissues.