Clonal selection
Encyclopedia
Immune system
An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...
responds to infection
Infection
An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...
and how certain types of B and T lymphocyte
Lymphocyte
A lymphocyte is a type of white blood cell in the vertebrate immune system.Under the microscope, lymphocytes can be divided into large lymphocytes and small lymphocytes. Large granular lymphocytes include natural killer cells...
s are selected for destruction of specific antigens invading the body.
Four predictions of the clonal selection hypothesis
- Each lymphocyte bears a single type of receptor with a unique specificity (by V(D)J recombinationV(D)J recombinationVJ recombination, also known as somatic recombination, is a mechanism of genetic recombination in the early stages of immunoglobulin and T cell receptors production of the immune system...
). - Receptor occupation is required for cell activation.
- The differentiated effector cells derived from an activated lymphocyte will bear receptors of identical specificity as the parental cell.
- Those lymphocytes bearing receptors for self molecules will be deleted at an early stage.
Early work
In 1954, immunologist Niels Jerne put forward a hypothesis which stated that there is already a vast array of lymphocytes in the body prior to any infection. 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 BurnetFrank Macfarlane Burnet
Sir Frank Macfarlane Burnet, , usually known as Macfarlane or Mac Burnet, was an Australian virologist best known for his contributions to immunology....
with input from David W. Talmage worked on this model, and was the first to name it "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
Gustav Nossal
Sir Gustav Victor Joseph Nossal, AC, CBE, FRS, FAA is an Australian research biologist.-Life and career:Gustav Nossal's family was from Vienna, Austria. He was born four weeks prematurely in Bad Ischl while his mother was on holiday...
and Joshua Lederberg showed that one B cell always produces only one antibody, which was the first evidence for clonal selection theory.
Theories supported by clonal selection
Burnet and Peter MedawarPeter Medawar
Sir Peter Brian Medawar OM CBE FRS was a British biologist, whose work on graft rejection and the discovery of acquired immune tolerance was fundamental to the practice of tissue and organ transplants...
worked together on understanding immunological tolerance, a phenomenon also explained by clonal selection. 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
Nobel Prize
The Nobel Prizes are annual international awards bestowed by Scandinavian committees in recognition of cultural and scientific advances. The will of the Swedish chemist Alfred Nobel, the inventor of dynamite, established the prizes in 1895...
for physiology
Physiology
Physiology is the science of the function of living systems. This includes how organisms, organ systems, organs, cells, and bio-molecules carry out the chemical or physical functions that exist in a living system. The highest honor awarded in physiology is the Nobel Prize in Physiology or...
and medicine
Medicine
Medicine is the science and art of healing. It encompasses a variety of health care practices evolved to maintain and restore health by the prevention and treatment of illness....
in 1960.
In 1974 Niels Kai Jerne proposed that the immune system functions as a network, that is regulated via interactions between the variable parts of lymphocytes and their secreted molecules. Immune network theory
Immune network theory
The immune network theory is a theory of how the adaptive immune system works, that has been developed since 1974 mainly by Niels Jerne and Geoffrey W. Hoffmann. The theory states that the immune system is an interacting network of lymphocytes and molecules that have variable regions...
is firmly based on the concept of clonal selection. Jerne won the Nobel Prize
Nobel Prize
The Nobel Prizes are annual international awards bestowed by Scandinavian committees in recognition of cultural and scientific advances. The will of the Swedish chemist Alfred Nobel, the inventor of dynamite, established the prizes in 1895...
for medicine
Medicine
Medicine is the science and art of healing. It encompasses a variety of health care practices evolved to maintain and restore health by the prevention and treatment of illness....
or physiology
Physiology
Physiology is the science of the function of living systems. This includes how organisms, organ systems, organs, cells, and bio-molecules carry out the chemical or physical functions that exist in a living system. The highest honor awarded in physiology is the Nobel Prize in Physiology or...
in 1984, largely for his contributions to immune network theory.
See also
- Immune systemImmune systemAn immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...
- Adaptive immune systemAdaptive immune systemThe adaptive immune system is composed of highly specialized, systemic cells and processes that eliminate or prevent pathogenic growth. Thought to have arisen in the first jawed vertebrates, the adaptive or "specific" immune system is activated by the “non-specific” and evolutionarily older innate...
- Clonal Selection AlgorithmClonal Selection AlgorithmIn Artificial immune systems, Clonal selection algorithms are a class of algorithms inspired by the clonal selection theory of acquired immunity that explains how B and T lymphocytes improve their response to antigens over time called affinity maturation...
- Universal DarwinismUniversal darwinismUniversal Darwinism refers to a variety of approaches that extend the theory of Darwinism beyond its original domain of biological evolution on Earth...