Antibodies

Antibodies

1. Antibodies

   • Proteins synthesised by B cells
   • When the body is invaded by non-self material, the B cells produce antibodies
   • React with antigens on the surface of the non-self material
     • Bind to them precisely
     • Highly specific
   • Each antibody has its own antigen

2. Antibody structure

   • Made of 4 polypeptide chains
     • One pair are long, called heavy chains
     • One pair are shorter, called light chains
   • Change shape by moving as if they have a hinge in the fork of the Y shape
   • Have a binding site
     • Forms antigen-antibody complexes here
     • Called the variable region
       • Different for every antibody
   • Constant region
     • Same in all antibodies

3. Monoclonal antibodies

   • A pathogen entering the body is likely to have lots of different antigens on its surface
   • Each antigen will induce a different B cell to multiply and clone itself
   • These clones will each produce a different antibody, collecttively known as polyclonal antibodies
   • Single type of antibody is known as a monoclonal antibody
   • Production
     • Expose a mouse to non-self material against which an antibody is required
     • The B cells in thhe mouse produce polyclonal antibodies, which are extracted from the mouses spleen
     • To enable B cells to divide outside of the body, they are mixed with a cell that divides readily outside of the body
     • Detergent is added to the mixture to break down the cell-surface membranes of both types of cell, enabling them to fuse together
     • Fused cells are separated under a microscope and each cell is cultured to form a group. Each clone is tested to see if it is producing the correct antibody
     • Any clone producing the correct antibody is grown on a large scale and antibdies are extracted from the growth medium
     • As they are from a mouse, the antibodies have to be modified to make them like human cells - humanisation

4. Ethical production and use of monoclonal antibodies

   • Involves use of animals
     • Used to produce both antibodies and tumour cells
     • Tumour cells - deliberately inducing cancer in animals
     • Guidelines to minimise suffering, but some still have reservations
   • Iliminate need for humanisation
     • Transgenic mice can be used
     • A human gene is placed into the mice
     • Ethics of genetic engineering
   • Treat diseases
     • Saving many lives
     • Some deaths associated with their use in the treatment of multiple sclerosis
   • Testing
     • In March 2006, 6 healthy volunteers took part in the trial of a new antibody
     • Within minutes they suffered multiple organ failure
     • All volunteers survive, but raises issues