T cells are a subset of lymphocytes that play a large role in the immune response. The abbreviation "T" stands for thymus, the organ in which their final stage of development occurs.

There are many types of T cells:

• Cytotoxic T cells (CD8⁺) destroy infected cells. These cells function as 'killer' or cytotoxic cells because they are able to destroy target cells which express specific antigens that they recognize.
• Helper T cells (CD4⁺) are "middlemen" in the immune response. When they get activated, they proliferate and secrete cytokines, that regulate or 'help' effector lymphocyte function. They are known as one of the targets of HIV infection, and the decrease of CD4⁺ T cells results in AIDS. Some helper T cells secrete cytokines that turn off the immune response once an antigen has been eliminated from the body.

Every effective immune response involves T cell activation, however they are especially important in cell-mediated immunity, that is the defence against pathogenic organisms inside body cells, tumor cells and is also involved in rejection reactions.

CD4 and CD8 refer to the characteristic antigens on the surface of the different sub-types of T-lymphocytes. These CD molecules are convenient diagnostic markers for identifying and quantitating these cells by flow cytometry using specific antibodies against them. T cell activity and secretions are frequently determined using the ELISPOT technique.

See also

• White blood cell

External links

• PLOS Primer: Antigen-Specific T Cells: Analyses of the Needles in the Haystack (http://www.plosbiology.org/plosonline/?request=get-document&doi=10.1371%2Fjournal.pbio.0000078)
• T Cell Workshop (http://www.idsoc.org/Octworkshop.html), Research by the Immunology of Diabetes Society

Immune system

Humoral immune system - Cellular immune system - Lymphatic system

White blood cells - B cells - Antibodies - Antigen (MHC)

Lymphocytes: T cells (Cytotoxic & Helper) - B cells (Plasma cells & Memory B cells)

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