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Lymphocytes

Biology: Cambridge International A Level, topic 11.1.3

T Lymphocytes

T lymphocyte cells are white blood cells that are involved in the cellular immune response. The steps involved in this process are:

1) Detection of antigens

1) Detection of antigens

  • The foreign antigens presented by phagocytes bind to specific receptors on the cell surface of T lymphocyte cells.
  • Binding of the antigens activates the T helper cells.
2) T helper cells

2) T helper cells

  • T helper (TH) cells are a specific type of T cell that activates several cells including:
  • Phagocytes.
  • T cytotoxic (TC) cells.
  • B cells.
3) T cytotoxic cells

3) T cytotoxic cells

  • TC cells are activated by TH cells.
  • TC cells release toxins that bind to and kill foreign cells and abnormal cells in the body.

Interleukins

  • T helper cells regulate the activity of other immune cells via the release of cytokines.
  • Cytokines are small proteins involved in cell signalling.
  • An important group of cytokines involved in regulating immune response are interleukins.
  • Interleukins can stimulate or suppress the action of other cells involved in the immune response.

B Lymphocytes

B lymphocyte cells are white blood cells that are involved in the humoral immune response. The steps involved in this process are:

1) Activation of B cells

1) Activation of B cells

  • TH cells activates B cells.
  • Activation of the B cells causes the B cells to divide into identical cells called plasma cells.
  • The production of plasma cells is called clonal selection.
2) Detection of antigens

2) Detection of antigens

  • B cells have specific proteins called antibodies on their cell surface membranes.
  • Each antibody is specific to a specific antigen.
  • When an antigen binds to an antibody, an antigen-antibody complex is formed.
  • Binding of antigens to B cells also causes clonal selection.
3) Plasma cells

3) Plasma cells

  • Clonal selection leads to the production of many plasma cells that have the specific antibodies for the antigens present in the body.
  • The antibodies are called monoclonal antibodies.
  • Monoclonal antibodies bind to the antigens of the pathogens.
4) Agglutination

4) Agglutination

  • Agglutination 'clumps' the pathogens together.
  • The pathogens are engulfed by phagocytes via phagocytosis.
  • The pathogens are destroyed.
White blood cell counts

White blood cell counts

  • Measuring white blood cell counts is important in medicine.
  • Raised white blood cell counts can indicate:
  • Recent infection. Pathogens stimulate an immune response, so an increase in white blood cell counts.
  • Certain cancers. Leukemia is a type of cancer that involves the uncontrolled growth of blood and bone marrow cells.
    • The type of white blood cells that have increases levels can indicate the type of leukemia.
    • For example, lymphocytic leukemia typically involves elevated B cell counts.

Test yourself on Lymphocytes

  • Which of these is NOT activated by T helper cells?

  • Which of the following statements about T lymphocytes are true?

  • What is the role of T cytotoxic cells?

  • Steps Involved in the Humoral Response

  • Which of the following statements about B lymphocytes are true?

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