Immunity

• Pathogen


  A disease-causing organism
• Ways pathogens can be passed on from host to host

  • Direct contact (e.g. HIV, gonorrhoea, hepatitis B & C)
  • Indirect contact (e.g. droplets in air, food/water, touching contaminated surfaces, insect bites)
• Mechanical barriers


  • Structures that make it difficult for pathogens to get past them and into the body.
• Chemical barriers


  • Substances produced by the body cells that trap/kill pathogens before they can get further into the body and cause disease (e.g. mucus, stomach acid)
• Cells


  • Different types of white blood cell work to prevent pathogens reaching areas of the body they can replicate in (e.g. by phagocytosis, producing antibodies)
• Antigen


  Proteins and other substances projecting from the cell membrane that are specific to that type of cell
• Antibody


  Made by lymphocytes, complementary shape to the antigens on the surface of pathogenic cells, cause agglutination and signal to phagocytes
• Immune response to pathogens

  1. Lymphocytes read antigens, make specific antibodies, form memory cells

  2. Memory cells quickly make more antibodies on reinfection
• Active immunity


  Making antibodies and developing memory cells for future response to infection
• Passive immunity


  Ready-made antibodies from another source are introduced to the body, fast-acting but short-term
• Occasionally, the immune system starts to attack the body's own cells, leading to diseases like Type 1 diabetes
• Vaccination


  Gives protection against specific diseases and boosts the body's defence against infection from pathogens without the need to be exposed to dangerous diseases
• Antigen


  A chemical found on the surface of a cell
• Antibody


  A chemical made by lymphocytes that is complementary to an antigen and, when attached, clumps them together and signals the cells they are on for destruction
• Antibiotic


  A drug that slows down or stops the growth of bacteria
• Vaccination


  Gives protection against specific diseases and boosts the body's defence against infection from pathogens without the need to be exposed to dangerous diseases that can lead to death
• Vaccines


  • Allow a dead or altered form of the disease-causing pathogen, which contains specific antigens, to be introduced into the body
  • In this weakened state, the pathogen cannot cause illness but can provoke an immune response
  • Lymphocytes produce complementary antibodies for the antigens
  • The antibodies target the antigen and attach themselves to it in order to create memory cells
  • The memory cells remain in the blood and will quickly respond to the antigen if it is encountered again in an infection by a 'live' pathogen
  • As memory cells have been produced, this immunity is long-lasting
• Herd immunity


  If a large enough percentage of the population is vaccinated, it provides protection for the entire population because there are very few places for the pathogen to breed – it can only do so if it enters the body of an unvaccinated person
• Smallpox has been officially eradicated in 1980 after a vaccination programme run by the World Health Organisation since the mid-1950s
• Measures to prevent spread of pathogens

  • Hygienic food preparation
  • Personal hygiene
  • Waste disposal
  • Sanitation
• Hygienic food preparation


  1. Keep food cold so bacteria and fungi reproduce more slowly

  2. Prepare food hygienically to avoid contamination from pathogens by washing hands well with soap and cleaning work surfaces with products such as bleach to kill pathogens

  3. Cook food well (long enough at high temperature) to kill bacteria and fungi

  4. Cover food to prevent flies landing on it before eating

  5. Use separate chopping boards/utensils for cutting uncooked meat

  6. Wash hands after using the bathroom before handling food