Clonal selection of lymphocytes: 1) A hematopoietic stem cell undergoes differentiation and genetic rearrangement to produce 2) immature lymphocytes with many different antigen receptors. A lymphocyte is a type of White blood cell in the Vertebrate Immune system. Hematopoietic stem cells (HSCs are Stem cells that give rise to all the blood cell types including Myeloid ( Monocytes and Macrophages, Neutrophils Those that bind to 3) antigens from the body's own tissues are destroyed, while the rest mature into 4) inactive lymphocytes. Most of these will never encounter a matching 5) foreign antigen, but those that do are activated and produce 6) many clones of themselves.

The clonal selection theory has become a widely accepted model for how the immune system responds to infection and how certain types of B and T lymphocytes are selected for destruction of specific antigens invading the body. An immune system is a collection of mechanisms within an Organism that protects against Disease by identifying and killing Pathogens and Tumor An infection is the detrimental Colonization of a host Organism by a foreign Species. A lymphocyte is a type of White blood cell in the Vertebrate Immune system. An antigen (from antibody-generating) or immunogen is a substance that prompts the generation of Antibodies and can cause an immune response

Early Work

In 1954, immunologist Niels Jerne put forward a theory which stated that there is already a vast array of lymphocytes in the body prior to any infection. Niels Kaj Jerne, FRS ( December 23, 1911 &ndash October 7, 1994) was a Danish ( English -born Immunologist The entrance of an antigen into the body results in the selection of only one type of lymphocyte to match it and produce a corresponding antibody to destroy the antigen.

This selection of only one type of lymphocyte results in it being cloned or reproduced by the body extensively to ensure there are enough antibodies produced to inhibit and prevent infection.

Further Work

Australian immunologist Frank Macfarlane Burnet with input from David W. Talmage worked on this model, and was the first to name it "clonal selection theory. Sir Frank Macfarlane Burnet, OM, AK, KBE (3 September 1899 – 31 August 1985 usually known as Macfarlane or Mac Burnet, was David W Talmage (born 1919 is an American immunologist He made significant contributions to the Clonal selection theory " Burnet explained immunological memory as the cloning of two types of lymphocyte. One clone acts immediately to combat infection whilst the other is longer lasting, remaining in the immune system for a long time, which results in immunity to that antigen. In 1958, Sir Gustav Nossal and Joshua Lederberg showed that one B cell always produces only one antibody, which was the first evidence for clonal selection theory. Sir Gustav Joseph Victor Nossal, AC, CBE, FRS, FAA (born June 4 1931) is an Australian research biologist ^[1]

Theories Supported by Clonal Selection

Burnet and Peter Medawar worked together on understanding immunological tolerance, a phenomenon also explained by clonal selection. Sir Peter Brian Medawar, OM, FRS, ( February 28, 1915 &ndash October 2, 1987) was a Brazilian born This is the organism’s ability to tolerate the introduction of cells without an immune response as long as this occurs early in the organism’s development. There are a vast number of lymphocytes occurring in the immune system ranging from cells which are tolerant of self tissue to cells which are not tolerant of self tissue. However, only cells that are tolerant to self tissue will survive the embryonic stage. If non-self tissue is introduced, the lymphocytes which develop will be the ones which included the non-self tissues as self tissue.

In 1949 Burnet proposed that under certain circumstances, tissues could be successfully transplanted into foreign recipients. This work has led to a much greater understanding of the immune system and also great advances in tissues transplantation. Burnet and Medawar shared the Nobel Prize for physiology and medicine in 1960. The Nobel Prize (Nobelpriset (Nobelprisen is a Swedish prize established in the 1895 will of Swedish chemist Alfred Nobel; it was first awarded in Peace, Literature Physiology (from Greek grc φύσις physis, "nature origin" and grc -λογία -logia) is the study of the mechanical physical Medicine is the art and science of healing It encompasses a range of Health care practices evolved to maintain and restore Human Health by the

References

1. ^ Nossal, G. J. V. & Lederberg, J. 1958. Antibody production by single cells. Nature 181:1419-1420

• "Biology in Context - The Spectrum of Life" Authors, Peter Aubusson, Eileen Kennedy.
• Forsdyke, D. R. 1995. The Origins of the Clonal Selection Theory of Immunity FASEB. Journal 9:164-66