negative selection

(noun)

The process by which T cells are screened so that those with a high affinity for binding to self antigens (and potentially causing autoimmunity) are destroyed.

Related Terms

Examples of negative 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.
    • Negative selection is the process that eliminates developing lymphocytes whose antigen receptors bind strongly to self antigens present in the lymphoid organs.
    • Both developing B cells and T cells are subject to negative selection during a short period after antigen receptors are expressed.
    • Negative selection of developing lymphocytes is an important mechanism for maintaining central tolerance.
    • Describe the importance of central and peripheral tolerance and distinguish between positive and negative clonal selection

  • Maturation of T Cells

    • T cells originate from hematopoietic stem cells in the bone marrow and undergo positive and negative selection in the thymus to mature.
    • The earliest thymocytes express neither CD4 nor CD8, and are therefore classed as double-negative (CD4-CD8-) cells.
    • The potentially autoimmune cells are removed by the process of negative selection.
    • Negative selection removes thymocytes that are capable of strongly binding with self-antigens presented by MHC.
    • These autoimmune disorders may be caused by problems in negative selection and tend to have genetic components.

  • Frequency-Dependent Selection

    • In frequency-dependent selection, phenotypes that are either common or rare are favored through natural selection.
    • Another type of selection, called frequency-dependent selection, favors phenotypes that are either common (positive frequency-dependent selection) or rare (negative frequency-dependent selection).
    • An interesting example of this type of selection is seen in a unique group of lizards of the Pacific Northwest.
    • An example of negative frequency-dependent selection can also be seen in the interaction between the human immune system and various infectious microbes such as pathogenic bacteria or viruses.
    • Negative frequency-dependent selection serves to increase the population's genetic variance by selecting for rare phenotypes, whereas positive frequency-dependent selection usually decreases genetic variance by selecting for common phenotypes.

  • Selective and Differential Media

    • Selective media are used for the growth of only selected microorganisms.
    • Selective growth media for eukaryotic cells commonly contain neomycin to select cells that have been successfully transfected with a plasmid carrying the neomycin resistance gene as a marker.
    • Some examples of selective media include:
    • Eosin methylene blue (EMB) that contains methylene blue – toxic to Gram-positive bacteria, allowing only the growth of Gram negative bacteria.
    • Xylose lysine desoxyscholate (XLD), which is selective for Gram-negative bacteria buffered charcoal yeast extract agar, which is selective for certain gram-negative bacteria, especially Legionella pneumophila.

  • Clonal Selection and T-Cell Differentiation

    • Antigens are "selected" to form clones of themselves, both memory and effector.
    • 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 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.

  • Asymmetric Information: Adverse Selection and Moral Hazard

    • This results in "bad" products or services being selected.
    • In addition to adverse selection, moral hazards are also a result of asymmetric information.
    • In relation to asymmetric information, moral hazard may occur if one party is insulated from risk and has more information about its actions and intentions than the party paying for the negative consequences of the risk.
    • A lack of equal information causes economic imbalances that result in adverse selection and moral hazards.
    • Examine the concept of adverse selection in the context of imperfect information

  • Antibiotics and Selective Toxicity

    • Antibiotics are able to selectively target specific types of bacteria without harming the infected host.
    • He then proposed the idea that it might be possible to create chemicals that would act as a selective drug that would bind to and kill bacteria without harming the human host.
    • More specifically, narrow spectrum antibiotics target specific types of bacteria, such as Gram-negative or Gram-positive bacteria, whereas broad spectrum antibiotics affect a wide range of bacteria.
    • The remainder must be tested for their selective toxicities and therapeutic activities, and the best candidates can be examined and possibly modified.
    • In antibacterial production, microorganisms must be isolated, cultured, and tested for growth inhibition of target organisms and for their selective toxicity.

  • Sampling from a population

    • In general, we always seek to randomly select a sample from a population.
    • The selected names would represent a random sample of 100 graduates.
    • Or perhaps her selection would be well-representative of the population.
    • If 50% of online reviews for a product are negative, do you think this means that 50% of buyers are dissatisfied with the product?
    • For this reason, we suspect there is a negative bias in product ratings on sites like Amazon.

  • Random Sampling

    • An online poll in which a person is asked to given their opinion about something is not random because only those people with strong opinions, either positive or negative, are likely to respond.
    • Some of these clusters are randomly selected.
    • Then, all the individuals in the chosen cluster are selected to be in the sample.
    • For example, while surveying households within a city, we might choose to select 100 city blocks and then interview every household within the selected blocks, rather than interview random households spread out over the entire city.
    • Online and phone-in polls also produce biased samples because the respondents are self-selected.