Edexcel A (SNAB) A Level Biology:复习笔记6.2.3 Non-specific Immune Responses

Non-specific Immune Responses

  • There are two types of immune response in the body once a pathogen enters
    • Non-specific
      • This response is the same, regardless of the pathogen that invades the body
    • Specific
      • This is a response specific to a particular pathogen
      • The immune system is able to recognise specific pathogens due to the presence of antigens on their cell surface
        • Antigens are molecules such as proteins or glycoproteins located on the surface of cells; their role is to act as an ID tag, identifying a cell as being 'self' or 'non-self'
          • Pathogens have non-self antigens, so the immune system recognises them as not belonging to the body
  • When a pathogen invades tissue the non-specific immune response begins immediately; this includes
    • Inflammation
    • Interferons
    • Phagocytosis

Inflammation

  • The surrounding area of a wound can sometimes become swollen, warm and painful to touch; this is inflammation
  • Body cells called mast cells respond to tissue damage by secreting the molecule histamine
    • Histamine is a chemical signalling molecule that enables cell signalling, or communication between cells
  • Histamine stimulates the following responses
    • Vasodilation increases blood flow through capillaries
    • Capillary walls become 'leaky', or more permeable, allowing fluid to enter the tissues and creating swelling
      • Some plasma proteins leave the blood when the capillaries become more permeable
    • Phagocytes leave the blood and enter the tissue to engulf foreign particles
    • Cells release cytokines, another cell signalling molecule that triggers an immune response in the infected area

Interferons

  • Cells infected by viruses produce anti-viral proteins called interferons
  • Interferons prevent viruses from spreading to uninfected cells
    • They inhibit the production of viral proteins, preventing the virus from replicating
    • They activate white blood cells involved with the specific immune response to destroy infected cells
    • They increase the non-specific immune response e.g. by promoting inflammation

Phagocytosis

  • Phagocytes are a type of white blood cell responsible for removing dead cells and invasive microorganisms; they do this by engulfing and digesting them
    • The process of engulfing and digesting is known as phagocytosis
  • Phagocytes travel throughout the body and can leave the blood by squeezing through capillary walls
  • During an infection they are released in large numbers
  • Mode of action
    • Chemicals released by pathogens, as well as chemicals released by the body cells under attack, e.g. histamine, attract phagocytes to the site where the pathogens are located
    • They move towards pathogens and recognise the antigens on the surface of the pathogen as being non-self
    • The cell surface membrane of a phagocyte extends out and around the pathogen, engulfing it and trapping the pathogen within a phagocytic vacuole
      • This part of the process is known as endocytosis
    • Enzymes are released into the phagocytic vacuole when lysosomes fuse with it
    • These digestive enzymes, which includes lysozyme, digest the pathogen
    • After digesting the pathogen, the phagocyte will present the antigens of the pathogen on its cell surface membrane
      • The phagocyte becomes what is known as an antigen presenting cell
    • The presentation of antigens initiates the specific immune response

Phagocytes engulf pathogens in the process of phagocytosis, enclosing them in a phagocytic vacuole. Lysosomes fuse with the vacuole, releasing enzymes which digest the pathogen.

 

 

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