Defence mechanisms


Defence mechanisms include:

  • Skin
  • Musus
  • Ear wax
  • Phagocytes - only attack pathogens
  • Tears - chemical
  • Stomach acid - chemical


  • An interaction between the pathogen and the body's various defence mechanisms


  • The body's defences are better prepared for a second infection from the same pathogen and can kill it before it can cause any harm


A type of white blood cell - takes two forms:

  • Cell-mediated responses involving T lymphocytes
  • Humoral responses involving B lymphocytes

Recognising your own cells:

  • Lymphocytes must be able to distinguish between the body's own cells from those that are foreign
  • Each type of cell has specific molecules on its surface to identify it
  • The proteins on the surface are the most important because they have a large variety and high specific tertiary structure
  • It is this variety of a specific 3-D structure that distinguishes one cell from another

It is usually the protein molecules that allow the immune system to identify -

  • Pathogens - for example HIV
  • Non-self material -


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