T lymphocytes and cell-mediated immunity



  • Any part of an organism or subtance that is recognised as foreign by the immune system and stimulates an immune respone
  • Usually proteins that are part of the cell-surafce membrans or cell walls of invading cells such as micro organisms or abnormal body cells
  • The presence of an antigen triggers the production of an antibody as part of the body's defence systems


  • Produced by stem cells in the bone marrow

T lymphocytes -

  • Mature in the thymus gland
  • Associated with cell-mediated immunity that is immunity involving body cells

Cell-mediated immunity: (cellular response)

  • T lymphocytes will only respond to antigens that are presented on body cells
  • The receptors on each T cell respond to a single antigen

Stages in the response of T lymphocytes to infection by a pathogen -

  • Pathogens invade body cells or are taken in by phagocytes
  • The phagocyte places antigens from the pathogen on its cell-surface membrane
  • Receptors on a specific T cell (Th cell) fit exactly onto these antigens
  • This attachment activates the T cell to divide rapidly by mitosis and form a clone


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