11.1.2

Antigens

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Antigens

The immune system responds to pathogens and other foreign bodies because of the presence of antigens.

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'Foreign' signals

  • Antigens are molecules (proteins and glycoproteins) that are present on the cell surface membrane of all cells.
  • Antigens signal to the immune system if the cells are 'foreign'.
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Specificity

  • Every cell has specific antigens.
  • The antigens bind to complementary receptors on the cell surface membrane of the immune cells.
  • If the antigens are 'foreign', this will induce an immune response.
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'Self' signals

  • Not all antigens induce an immune response.
  • Antigens can also signal if the cells are 'self' or they belong to the host organism.
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Response

  • The immune system can respond to antigens in a number of ways:
    • Lysozymes break down the foreign cells.
    • Phagocytosis of the foreign cells.
    • Production of antibodies that bind to the antigens and inhibit the functioning of the foreign cells.
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Autoimmune responses

  • Sometimes the immune system fails to differentiate between self and non-self.
  • This can lead to the development of autoimmune conditions. In these conditions, the body's own immune system attacks the body's cells.
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Myasthenia gravis

An example of an autoimmune condition is myasthenia gravis.

  • In myasthenia gravis, the body produces antibodies against the acetylcholine receptor.
  • This receptor is found at the neuromuscular junction between nerves and muscles.
  • So, symptoms of this condition include paralysis and muscle weakness.
  • The first muscles that typically lose strength are those around the eye, leading to eyelid drooping,

Jump to other topics

1Cell Structure

2Biological Molecules

3Enzymes

4Cell Membranes & Transport

5The Mitotic Cell Cycle

6Nucleic Acids & Protein Synthesis

7Transport in Plants

8Transport in Mammals

9Gas Exchange

10Infectious Diseases

11Immunity

12Energy & Respiration (A2 Only)

13Photosynthesis (A2 Only)

14Homeostasis (A2 Only)

15Control & Coordination (A2 Only)

16Inherited Change (A2 Only)

17Selection & Evolution (A2 Only)

18Classification & Conservation (A2 Only)

19Genetic Technology (A2 Only)

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