T cell

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.

Related Topics:
Lymphocyte - Immune response - Thymus

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• 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.
• Regulatory T cells (also known as suppressor T cells) suppress activation of the immune system and maintain immune system homeostasis. Failure of regulatory T cells to function properly may result in autoimmune diseases in which the immunocytes attack healthy cells in the body.

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

Related Topics:
Cell-mediated immunity - Pathogen - Rejection reaction

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CD4 and CD8 refer to the characteristic antigens on the surface of the different sub-types of T-lymphocytes. These CD molecules (or Clusters of Differentiation) 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.

Related Topics:
Antigen - CD molecules - Flow cytometry - Antibodies - ELISPOT

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T cell: T cell development ►