Discovery of antibodies.

Passive immunisation has been used in clinical practice since the end of last century, mainly for prophylaxis. Success of early treatments was marred by anaphylactic reactions and serum sickness because antibodies or antitoxins were not raised in humans. Recombination of gene segments during antibody synthesis means that specific antibodies for numerous antigens can be produced from a limited gene pool. Killer lymphocytes, phagocytes, and complement then bind to the constant region of the antibody facilitating elimination of the pathogen. Development of a method of obtaining large quantities of antibodies against a specific antigen (monoclonal antibodies) offers the possibility of initiating host defence mechanisms against any unwanted antigen, though some problems still remain in preventing the body from attacking the monoclonal antibody.