Microorganisms and cells, foreign to the body, such as disease-causing bacteria and viruses and other infectious agents,(pathogens) as well as foreign cells (as in transplants) and tumors can be recognized by the body's immune system. Our natural defenses include antibodies, proteins that seek out the pathogens and foreign cells and help destroy them.
Antibodies have two very useful characteristics. First, they are exquisitely specific; that is, each antibody binds to only a small portion of a pathogen or foreign cell and not related organisms or cells. Second, an antibody response, once activated by the occurrence of a disease, continues to attack and confer resistance against that disease; classic examples are the antibodies to the childhood diseases chickenpox and measles.
The latter characteristic of antibodies makes it possible to develop vaccines. A vaccine is a preparation of killed or weakened bacteria or viruses or tumor cells that, when introduced into the body, stimulates the production of antibodies against the live apathogens.
It is the first trait of antibodies, their specificity that makes monoclonal antibody technology so valuable. Not only can antibodies be used therapeutically, to protect against disease; they can also help to diagnose a wide variety of illnesses, and can detect the presence of drugs, viral and bacterial products, and other unusual or abnormal substances in the blood.
Given such a diversity of uses for these disease-fighting substances, their production in pure quantities has long been the focus of scientific investigation. The conventional method was to inject a laboratory animal with an antigen and then, after antibodies had been formed, collect those antibodies from the blood serum (antibody-containing blood serum is called "antiserum"). There are two problems with this method: It yields antiserum that contains undesired substances, and it provides a very small amount of usable antibody. Monoclonal antibody technology allows us to produce large amounts of pure antibodies.
