Download The clonal selection hypothesis is a widely accepted

The clonal selection hypothesis is a widely accepted model for the
immune system's response to infection.
LEARNING OBJECTIVE [ edit ]
Describe the clonal selection hypothesis in regards to the production of B cells
KEY POINTS [ edit ]
In 1954, immunologist Niels Jerne put forth the hypothesis that there is already a vast array
of lymphocytes in the body beforeinfection. 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 it.
B cells exist as clones derived from a particular cell. Thus the antibodies and their differentiated
progenies can recognize and/or bind the same specific surface components composed of
biological macromolecules of a given antigen. Clonality has important consequences for
immunogenic memory.
The clonal selection hypothesis states that an individual B cell expresses receptors specific to the
distinct antigen, determined before the antibody ever encounters the antigen.
TERMS [ edit ]
clonal selection
An hypothesis which states that an individual lymphocyte (specifically, a B cell) expresses
receptors specific to the distinct antigen, determined before the antibody ever encounters the
antigen. Binding of Ag to a cell activates the cell, causing a proliferation of clone daughter cells.
clone
A group of identical cells derived from a single cell.
Give us feedback on this content: FULL TEXT [edit ]
The clonal selection hypothesis has
become a widely accepted model for how
theimmunesystem responds to infection
and how certain types of B and T
lymphocytes are selected for destruction of
specific antigens invading the body .
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A schematic view of clonal selection
Clonal selection of lymphocytes: 1) A hematopoietic stem cell undergoes differentiation and genetic
rearrangement to produce 2) immature lymphocytes with many different antigen receptors. 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.
Four predictions of the clonal selection hypothesis
Each lymphocyte bears a single type of receptor with a unique specificity (by V(D)J
recombination).
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.
In 1954, Danish 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. 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. " 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.
B cells exist as clones. All B cells derive from a particular cell, and as such, the antibodies and
their differentiated progenies can recognize and/or bind the same specific surface
components composed of biological macromolecules (epitope) of a given antigen. Such
clonality has important consequences, as immunogenic memory relies on it . The great
diversity in immune response comes about due to the up to 109 clones with specificities for
recognizing different antigens. Upon encountering its specific antigen, a single B cell, or a
clone of cells with shared specificity, divides to produce many B cells. Most of such B cells
differentiate into plasma cells that secrete antibodies into blood that bind the same epitope
that elicitedproliferation in the first place. A small minority survives asmemory cells that can
recognize only the same epitope. However, with each cycle, the number of surviving memory
cells increases. The increase is accompanied by affinity maturation which induces the
survival of B cells that bind to the particular antigen with high affinity. This subsequent
amplification with improved specificity of immune response is known as secondary immune
response. B cells that have not been activated by antigen are known as naive lymphocytes;
those that have met their antigen, become activated, and have differentiated further into fully
functional lymphocytes are known as effector B lymphocytes.
Hematopoiesis in Humans
This diagram shows hematopoiesis as it occurs in humans.