5 B lymphocytes and humoral immunity

  • Created by: lee8444
  • Created on: 04-03-20 11:27

Humoral immunity

  • Involves antibodies
  • Antibodies are soluble in blood and tissue fluid
  • Body fluids used to be called 'humour'
  • 10 million types of B cell
  • Each type of B cell produce a different type of antibody
  • Each specific antibody responds to one specific antigen
  • When an antigen enters the blood, there will be an antibody that is complementary to this on the surface of a B cell
  • The antigen enters the B cell by endocytosis
  • The antigen is presented on its cell-surface membrane
  • T helper cells bind to this which stimulates the B cell to divide by mitosis forming clones of the B cell
  • All of these B cells produce the specific antibody that is complementary to the pathogen's antigens
  • This clonals selection allows for rapid response to many antigens
  • A pathogen may have many different antigens on its surface
  • Some pathogens such as the cholera bacteria produce toxins which can act as antigens
  • The antibodies produced from clonal selection are called monoclonal antibodies
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Types of B cell

  • Plasma cells
    • secrete antibodies into blood plasma
    • only survive for a few days
    • makes 2000 antibodies per second
    • the antibodies produced lead to the destruction of of the antigen
    • responsible for immediate defense
    • primary response
  • Memory cells
    • secondary response
    • live considerably longer - around 50 years
    • don't produce antibodies
    • when they encounter an antigen, they divide rapidly
    • they develop into plasma cells and more memory cells
    • the plasma cells then produce the antibodies which responds to the infection
    • provides long-term immunity
    • quicker response than the primary response as it is ready
    • often no symptoms of infection
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How B cells provide immunity

1) Surface anigens of an invading pathogen are taken in by a B cell

2) B cell processes them and presents them on its cell-surface

3) Helper T cells attach to these antigens activating the B cell

4) B cell divides rapidly by mitosis to give clones of plasma cells

5) Cloned plasma cells produce thousands of antibodies

6) Antibodies attach to antigens of the pathogen and destroys them

7) Some of the B cells produced from mitosis develop into memory cells to provide long-term immunity. They respond to the same antigen as before and they can divide to produce plasma cells if needed for a secondary immune response which is rapid

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