clonal selection

(noun)

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.

Related Terms

Examples of clonal selection in the following topics:

  • Clonal Selection and Tolerance

    • Clonal selection and tolerance select for survival of lymphocytes that will protect the host from foreign antigens.
    • Clonal selection occurs after immature lymphocytes express antigen receptors.
    • The preservation of useful specificities is called positive selection.
    • clonal selection of the B and T lymphocytes:1.
    • Describe the importance of central and peripheral tolerance and distinguish between positive and negative clonal selection

  • Clonal Selection and T-Cell Differentiation

    • Clonal selection is an theory that attempts to explain why lymphocytes are able to respond to so many different types of antigens.
    • Clonal selection assumes that lymphocytes already have receptors for that antigen, and are selected during antigen presentation because they already have that unique antigen receptor.
    • Clonal selection means that an antigen is presented to many circulating naive B and (via MHC) T cells, and that the lymphocytes that match the antigen are "selected" to form clones of themselves, both memory and effector.
    • Clonal selection may also be used during negative selection during T cell maturation.
    • Clonal selection is thought to cause mutations of antigen binding affinity in memory cells during clonal expansion, so that memory cells have greatly increased antigen binding affinity than the effector cells during the first response.

  • Clonal Selection of Antibody-Producing Cells

    • The clonal selection hypothesis is a widely accepted model for the immune system's response to infection.
    • The clonal selection hypothesis 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 .
    • 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.
    • 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.
    • Describe the clonal selection hypothesis in regards to the production of B cells

  • Clonal Selection and B-Cell Differentiation

    • B Cells develop in way that is similar but different to T cells, and undergo clonal selection
    • This is a form of positive selection.
    • They are also tested for autoreactivity through negative selection.
    • Clonal selection is theory in which it is postulated that a B cell expresses antigen specific receptors before antibodies even encounter an antigen or before that antigen is ever found in the body.
    • Following the initial infection, random mutations during clonal selection could have produced memory B cells that can more easily bind to antigens than the original B cells could.

  • Specific T-Cell Roles

    • Differentiation into helper T cell subtypes occurs during clonal selection following T cell activation of naive T cells.
    • Their major role is to shut down T cell-mediated immunity toward the end of an immune reaction and to suppress auto-reactive T cells that escaped the process of negative selection in the thymus.

  • Immunological Memory

    • Memory cells derive from their parent B and T cells, and undergo clonal selection following infection, which increases their antigen binding affinity.

  • Maturation of T Cells

    • As the thymus shrinks in terms of functional mass by about 3% a year throughout middle age, there is a corresponding fall in the thymic production of naive T cells, leaving clonal expansion of immature T cells to play a greater role in protecting older subjects.
    • Positive selection "selects for" T cells capable of interacting with MHC.
    • A thymocyte's differentiation into helper or cytotoxic versions is also determined during positive selection.
    • Double-positive cells (CD4+/CD8+) that are positively selected on MHC class II molecules will eventually become CD4+ helper T cells, while cells positively selected on MHC class I molecules mature into CD8+ cytotoxic T cells.
    • The potentially autoimmune cells are removed by the process of negative selection.

  • Lymphocytes

    • They have an immunosupressive effect, in which they shut down cell mediated immunity at the end of a response, and act to destroy autoimmune T cells that aren't filtered out by negative selection in the thymus.
    • While in the bone marrow, B cells are sorted through positive and negative selection in  a manner similar but different from T cell maturation in the thymus, with the same process of killing B cells that are either nonreactive to antigens or reactive to self antigens.
    • Instead of apoptosis, defective B cells are killed through various mechanisms, such as clonal deletion.

  • Antimicrobial Peptides

    • In contrast to the clonal, acquired adaptive immunity, endogenous peptide antibiotics or antimicrobial peptides provide a fast and energy-effective mechanism as front-line defense.

  • The Heat-Shock Response

    • This is an example of small heat shock proteins produced by Pseudomonas aeruginosa Clonal Variants Isolated from Diverse Niches.