The Immune System

• An antibody is a protein molecule which fits into another molecule
• Pathogen molecules are called antigens.
• To destroy a pathogen, antibody molecules must be made which are exactly the right shape to fit into molecules (antigens) on the outside of the pathogen.
• Antibodies lock onto antigens leading to destruction of pathogen / marking of pathogens for destruction by phagocytes
• If a pathogen enters the body, it meets a large number of lymphocytes. One of these will recognize the pathogen and divide rapidly by mitosis
• These lymphocytes then secrete antibody, destroying the pathogens
• Active immunity: defence against a pathogen by antibody production in the body.
• Active immunity is gained after an infection by a pathogen or by vaccination.
• Vaccines immunise children against diseases caused by pathogens
• Process of vaccination:

  • Harmless pathogen given which has antigens
  • Antigens trigger an immune response by lymphocytes which produce antibodies
  • Memory cells are produced that give long term immunity
• In controlling the spread of disease, it is important to consider hygienic food preparation, good personal hygiene, waste disposal and sewage treatment
• Passive immunity: short term defence against a pathogen by antibodies acquired from another individual, e.g. mother to infant
• Memory cells are not produced in passive immunity
• Babies get passive immunity by breast feeding.

  • Breast milk contains antibodies from the mother which are passed on to her baby.
  • Useful because a young baby’s immune system is not well developed and so the mother’s antibodies can protect it against any diseases to which she is immune for the first few months of its life
• Some diseases are caused by the immune system targeting and destroying body cells (Type 1 diabetes)