Immunity and cell recognition

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  • Created by: Eema003
  • Created on: 25-02-16 15:27

Defence mechanisms

The body has two types of defences to protect itself from pathogens.

  • General and immediate barriers such as skin, to stop entry of pathogens.
  • More specific, less rapid and longer-lasting.

Specific defences involve a type of white blood cell; lymphocytes.

  • TH cells - Cell-mediated response
  • TC cells- Cell- mediated response
  • B cells- Humoral response.
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How lymphocytes recognise self

  • In foetus, lymphocytes are constantly colliding with each other.
  • Infection in the foetus is rare- due to placenta.
  • Threfore lymphocytes almost exclusively collide with self material.
  • Some lymphocytes have receptors that fit those of the body's cells.
  • Those lymphocytes either die or are suppressed.
  • The lymphocytes that are left must fit non-self material. Therefore only respond to non-self.
  • In adults Lymphocytes produced in the bone marrow initially only encounter self-antigens.
  • Any lymphocytes that show an immune response to these self-antigens undergo apoptosis (programmed cell death), before they can mature lymphocytes.
  • No clones of these anti-self lymphocytes will appear in the blood, leaving only those that might respons to non-self antigens.
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  • The phagocyte is attracted to the pathogen as it releases chemical products.Therefore the phagocyte then moves towards to the pathogen.
  • Phagocytes have serveral receptors on their cell-surface membrane that recognise, and attach to, chemicals on the surface of the pathogen.
  • They engluf the pathogen to form a phagosome.
  • Lysosomes move towards the phagosome and fuse with it.
  • Lysozymes destroy the ingested bacteria by hydrolysis of their cell walls
  • The soluble products from the breakdown of the pathogen are absorbed into the cytoplasm of the phagocyte.
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B- lymphocytes-  They mature in the bone marrow. Involed in humoral immunity- which is immunity involving antibodies that are present in fluids.

T-lymphocytes- They mature in the thymus gland. Involved in Cell-mediated immunity- which is immunity involving body cells.

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