cytotoxic T cell

(noun)

a subgroup of lymphocytes (white blood cells) that are capable of inducing death to infected somatic or tumor cells; part of cell-mediated immunity

Related Terms

Examples of cytotoxic T cell in the following topics:

  • Cell-Mediated Immunity

    • Cell-mediated immunity involves cytotoxic T cells recognizing infected cells and bringing about their destruction.
    • Unlike B cells, T lymphocytes (T cells) are unable to recognize pathogens without assistance.
    • Cytotoxic T cells mediate one arm of the cellular immune response
    • There are two main types of T cells: helper T lymphocytes (TH) and the cytotoxic T lymphocytes (TC).
    • The TH lymphocytes function indirectly to tell other immune cells about potential pathogens, while cytotoxic T cells (TC) are the key component of the cell-mediated part of the adaptive immune system which attacks and destroys infected cells.

  • Immunodeficiency

    • This response is accompanied by a marked drop in the number of circulating CD4+ T cells, cells that are or will become helper T cells.
    • The CD8+ T cell response is thought to be important in controlling virus levels, which peak and then decline, as the CD4+ T cell counts recover.
    • Ultimately, HIV causes AIDS by depleting CD4+ T cells (helper T cells).
    • T cells are essential to the immune response; without them, the body cannot fight infections or kill cancerous cells.
    • During the acute phase, HIV-induced cell lysis and killing of infected cells by cytotoxic T cells accounts for CD4+ T cell depletion, although apoptosis (programmed cell death) may also be a factor.

  • Antibody Functions

    • Differentiated plasma cells are crucial players in the humoral immunity response.
    • Once secreted, antibodies circulate freely and act independently of plasma cells.
    • Antibody neutralization can prevent pathogens from entering and infecting host cells, as opposed to the cytotoxic T-cell-mediated approach of killing cells that are already infected to prevent progression of an established infection.
    • Antibodies also mark pathogens for destruction by phagocytic cells, such as macrophages or neutrophils, because they are highly attracted to macromolecules complexed with antibodies.
    • Conversely, antibodies raised against pathogenic molecular components that resemble self molecules may incorrectly mark host cells for destruction, causing autoimmune damage.

  • Cytotoxic T Lymphocytes and Mucosal Surfaces

    • Most cells in the blood are red blood cells.
    • B cell maturation occurs in the bone marrow, whereas progenitor cells migrate from the bone marrow and develop and mature into naïve T cells in the organ called the thymus.
    • On maturation, T and B lymphocytes circulate to various destinations.
    • Lymph nodes scattered throughout the body house large populations of T and B cells, dendritic cells, and macrophages .
    • The spleen houses B and T cells, macrophages, dendritic cells, and NK cells .

  • Antigen-presenting Cells: B and T cells

    • Whether an immature lymphocyte becomes a B cell or T cell depends on where in the body it matures.
    • The B cells remain in the bone marrow to mature (hence the name "B" for "bone marrow"), while T cells migrate to the thymus, where they mature (hence the name "T" for "thymus").
    • Meanwhile, T cell receptors are responsible for the recognition of pathogenic antigens by T cells .
    • Unlike B cells, T cells do not directly recognize antigens.
    • Explain the role played by B and T cells in the adaptive immune system

  • Natural Killer Cells

    • While NK cells are part of the innate immune response, they are best understood relative to their counterparts in the adaptive immune response,T cells, which are also classified as lymphocytes.
    • T cells are lymphocytes that mature in the thymus gland and identify intracellular infections, especially from viruses, by the altered expression of major histocompatibility class (MHC) I molecules on the surface of infected cells.
    • If the cell is infected, the MHC I molecules display fragments of proteins from the infectious agents to T-cells.
    • This process can deplete host MHC I molecules on the cell surface, which prevents T-cells from recognizing them, but which NK cells detect as "unhealthy" or "abnormal" while searching for cellular MHC I molecules.
    • As such, NK cells offer a complementary check for unhealthy cells, relative to T cells.

  • Immunological Memory

    • During the adaptive immune response to a pathogen that has not been encountered before, known as the primary immune response, plasma cells secreting antibodies and differentiated T cells increase, then plateau over time.
    • As B cells and T cells mature into effector cells, a subset of the naïve populations differentiates into B and T memory cells with the same antigen specificities .
    • A memory cell is an antigen-specific B or T lymphocyte that does not differentiate into an effector cell during the primary immune response, but that can immediately become an effector cell on re-exposure to the same pathogen.
    • A helper T cell recognizes the MHC II–antigen complex and activates the B cell.
    • Describe the role of memory B and T cells in immulogical memory

  • Cell Signaling and Cell Death

    • Another example of external signaling that leads to apoptosis occurs in T-cell development.
    • T-cells are immune cells that bind to foreign macromolecules and particles, targeting them for destruction by the immune system.
    • Normally, T-cells do not target "self" proteins (those of their own organism), a process that can lead to autoimmune diseases.
    • In order to develop the ability to discriminate between self and non-self, immature T-cells undergo screening to determine whether they bind to so-called self proteins.
    • If the T-cell receptor binds to self proteins, the cell initiates apoptosis to remove the potentially dangerous cell.

  • White Blood Cells

    • They include B cells, T cells, and natural killer cells.
    • T cells attack viruses, fungi, some bacteria, transplanted cells, and cancer cells.
    • Once inside the cell, HIV then multiplies using the T cell's own genetic machinery.
    • After the HIV virus replicates, it is transmitted directly from the infected T cell to macrophages.
    • Lymphocytes, including B and T cells, are responsible for adaptive immune response.

  • Regulating Immune Tolerance

    • Immune tolerance of self and harmless antigens occurs by deleting B and T cells that recognize those antigens, often near mucosal surfaces.
    • There are populations of T cells that suppress the immune response to self-antigens.
    • Antigen-presenting cells, T cells, and B cells aggregate within the Peyer's patch, forming organized lymphoid follicles.
    • There, some T cells and B cells are activated.
    • Other antigen-loaded dendritic cells migrate through the lymphatic system where they activate B cells, T cells, and plasma cells in the lymph nodes.