Meezy asked in Science & MathematicsBiology · 1 decade ago

What is a T cell?

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  • 1 decade ago
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    T cells belong to a group of white blood cells known as lymphocytes and play a central role in cell-mediated immunity. They can be distinguished from other lymphocyte types, such as B cells and NK cells by the presence of a special receptor on their cell surface that is called the T cell receptor (TCR). The abbreviation "T", in T cell, stands for thymus since it is the principal organ for their development.

    Several different subsets of T cells have been described, each with a distinct function.

    Helper T cells are the "middlemen" of the adaptive immune system. Once activated, they divide rapidly and secrete small proteins called cytokines that regulate or "help" the immune response. These cells (also called CD4+ T cells) are a target of HIV infection; the virus infects the cell by using the CD4 protein to gain entry. The loss of Th cells as a result of HIV infection leads to the symptoms of AIDS.

    Cytotoxic T cells (Tc cells) destroy virally infected cells and tumor cells, and are also implicated in transplant rejection. These cells are also known as CD8+ T cells, since they express the CD8 glycoprotein at their surface.

    Memory T cells are a subset of antigen-specific T cells that persist long-term after an infection has resolved. They quickly expand to large numbers of effector T cells upon re-exposure to their cognate antigen, thus providing the immune system with "memory" against past infections. Memory T cells comprise two subtypes: central memory T cells (TCM cells) and effector memory T cells (TEM cells). Memory cells may be either CD4+ or CD8+.

    Regulatory T cells (Treg cells), formerly known as suppressor T cells, are crucial for the maintenance of immunological tolerance. Their major role is to shut down T cell mediated immunity towards the end of an immune reaction and to suppress auto-reactive T cells that escaped the process of negative selection in the thymus. Two major classes of regulatory T cells have been described, including the naturally occurring Treg cells and the adaptive Treg cells. Naturally occurring Treg cells (also known as CD4+CD25+FoxP3+ Treg cells) arise in the thymus, whereas the adaptive Treg cells (also known as Tr1 cells or Th3 cells) may originate during a normal immune response. Naturally occurring Treg cells can be distinguished from other T cells by the presence of an intracellular molecule called FoxP3. Mutations of the FOXP3 gene can prevent regulatory T cell development, causing the fatal autoimmune disease IPEX.

    Natural Killer T cells (NKT cells) are a special kind of lymphocyte that bridges the adaptive immune system with the innate immune system. Unlike conventional T cells that recognize peptide antigen presented by major histocompatibility complex (MHC) molecules, NKT cells recognize glycolipid antigen presented by a molecule called CD1d. Once activated, these cells can perform functions ascribed to both Th and Tc cells (i.e. cytokine production and release of cytolytic/cell killing molecules).

    γδ T cells represent a small subset of T cells that possess a distinct TCR on their surface. A majority of T cells have a TCR composed of two glycoprotein chains called α- and β- TCR chains. However, in γδ T cells, the TCR is made up of one γ-chain and one δ-chain. This group of T cells is much less common (5% of total T cells) than the αβ T cells, but are found at their highest abundance in the gut mucosa, within a population of lymphocytes known as intraepithelial lymphocytes (IELs). The antigenic molecules that activate γδ T cells are still widely unknown. However, γδ T cells are not MHC restricted and seem to be able to recognise whole proteins rather than requiring peptides to be presented by MHC molecules on antigen presenting cells. Some recognize MHC class IB molecules though. Human Vγ9/Vδ2 T cells, which constitute the major γδ T cell population in peripheral blood, are unique in that they specifically and rapidly respond to a small non-peptidic microbial metabolite, HMB-PP, an isopentenyl pyrophosphate precursor.

    Source(s): wikipedia
  • 1 decade ago

    An easy explaination: T cell is a mature lymphocyte. It matures in the thymus. It's main role is to regulate immune function. The T cell acts as a "killer cell" to anything that your body recognizes as non-self!

  • 1 decade ago

    A T Cell is a part of the immune system and it attacks a virus or bacteria.

    Source(s): I took Biology last year.
  • 1 decade ago

    It is a type of white blood cell that protects you from other terrorist cells...like cancer...and the like.

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  • aqua
    Lv 4
    1 decade ago

    a lymphocyte responsible for cell mediated immunity

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