5 T lymphocytes & cell-mediated immunity

  • Created by: lee8444
  • Created on: 03-03-20 09:06


  • Antigens - any part of an organism or substance that is recognised as foreign by the immune system
  • Stimulates an immune response
  • Usually proteins on the cell-surface membrane or cell wall
  • Can be on invading cells such as microorganisms or abnormal cells such as cancel cells
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Types of lymphocyte

  • Non-specific responses include phagocytosis and happen no matter whta the infection is
  • Specific responses react to specific antigens
    • slower at first
    • provide long term immunity
    • depends on what type of white blood cell (lymphocyte)
    • lymphocytes are produced by stem cells in bone marrow
  • B lymphocytes
    • mature in bone marrow
    • humoral immunity
    • immunity involving antibodies that are present in body fluids of 'humour' such as blood plasma
  • T lymphocytes
    • mature in the thymus gland
    • cell-mediated immunity
    • immunity involving body cells
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Cell-mediated immunity

  • Responded to an organisms own infected cells
  • These cells have been infected by non-self material such as a virus and cancers as they are genetically different
  • These cells therefore have different antigens than the organism's own cells
  • T lymphocytes can distinguish invader cells from normal cells because
    • phagocytes have engulfed and hydrolysed a pathogen and they are presenting the pathogen's antigens on its own cell-surface membrane
    • body cells invaded by a virus present some of the viral antigens on their own cell-surface membrane
    • transplanted cells from another individual with have different antigens on its cell-surface membrane
    • cancer cells are different genetically and so present different antigens on their cell-surface membrane
  • Cell displaying foreign antigens are called antigen-presenting cells
  • T lymphocytes only respond to antigen-presenting cells rather than antigens in body fluids
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T lymphocyte response

1) Pathogens invade body cells or are taken in by phagocytes

2) Phagocyte places antigens from the pathogen on its cell-surface membrane

3) Receptors on specific helper T cell fit exactly onto these antigens

4) Attachment activates the T cell to divide rapidly via mitosis and form a clone of genetically identical cells

5) Cloned T cells

a) develop into memory cells for a secondary response

b) stimulate phagocytes to engulf pathogens via phagocytosis

c) stimulate B cells to divide and secrete their antibody

d) activate cytotoxic T cells

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Cytotoxic T cells

  • Cytotoxic T cells kill abnormal cells and body cells that are infected by pathogens
  • They produce a protein called perforin
  • This makes holes in the cell-surface membrane
  • This causes the membrane to be freely permeable to all substances
  • This causes the rapid diffusion of many substances
  • Therefore, the cell dies
  • T cells are very important in protecting against a virus because viruses replicate inside host cells
  • Therefore, sacrificing host cells to stop the spread of the virus is essential for the survival of organisms
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