Clone selection theory
The clonal selection ( engl. Clonal selection theory in) describes Immunology the phenomenon that all of the cells, the specific antibody can produce ( B-lymphocyte ), as well as their corresponding cells ( T-lymphocyte ) clones are of a common parent cell.
Through contact with a certain antigen , from the innate multitude of these immunological mother cells (precursor cells), only that clone is stimulated to multiply which can bind the epitope of the antigen through a suitable receptor. This selective signal for so-called B-cell proliferation occurs at the molecular level in that a T -lymphocyte binds to an MHC protein (class I or class II) of a macrophage or B-lymphocyte that binds the Antigen presented after ingestion and preparation. After this binding and the release of interleukin-2 by the T cell, the antigen presenting cell (B lymphocyte or macrophage) initially begins to divide uninhibited. The progeny cells of this originally antigen-binding cell thus represent a clonal population. During division, they differentiate into antibody-producing cells ( plasma cells ) and memory cells .
Theoretically, every human has around 10 12 variants of the precursor cells capable of antigen recognition and can theoretically also form this (and only this) number of different antibodies. This innate population forms the so-called preimmune antibody repertoire. The different characteristics of these variants in different individuals also explains that in an epidemic , a statistical percentage of infected people always have an efficient immunity against the pathogen, since they happen to have the corresponding cellular clones.
The multitude of different mother cells far exceeds the number of all genes present in the human genome, from around 20,000 to 24,000 . The variations in antibody specificity occur through so-called somatic mutation or intramolecular recombination, whereby different genes for the protein chains of the antibodies are recombined and for the variable part there is a so-called fragmented gene , with several hundred gene fragments being variably chained to one another at different locations in the genome , combined and read with different reading grids ( frameshift ).
The clone selection theory was developed by Frank Macfarlane Burnet in 1957 by merging the side chain theory of Paul Ehrlich and the Jerne theory. It is often incorrectly referred to colloquially as "clonal selection".
literature
- Frank Macfarlane Burnet The clonal selection theory of acquired immunity , Cambridge University Press 1959
- Burnet Self and Non Self , Cambridge University Press 1969