Immune system, Herd immunity - EDITED

Immune system

A network of cells, tissues, and organs that work together to defend the body against attacks by pathogens

Innate immune system (non-specific)

• Can respond to threats to the body in minutes
  
• has limited capacity for recognition of foreign material
  
• form body's first line of defense
  
• involves skin, lysozyme, clotting of blood, mucus, stomach acid, phagocytes
• examples of phagocytes:
  

Adaptive immune system (specific)

• can respond in an almost infinitely flexible manner
• depends on antigenic stimulation
  
• Has memory, i.e. capable of remembering an encounter with a microbe or other foreign substance, and can respond much more rapidly at the second encounter.
  
• Involves:
  
  • Production of antibodies
    
  • Killing of virally infected cells
    
• Involves lymphocytes

Immunity

• Active immunity (acquired immunity)
  
  • Natural
    
  • Artificial
    
    • vaccination
      
• Passive immunity
  
  • Natural
    
    • Antibodies obtained through breast feeding
      
  • Artificial
    
    • Antibodies injected into the body
      

Herd immunity

• If enough people in a community are immunised against certain diseases, then it is more difficult for that disease to get passed between those who aren't immunised.
  
• If most people around you are immune to an infection and can't get sick, then there is no one around to infect you, even if you aren't immune to the infection.
  
• Only apply to diseases that can be passed on from person to person
  
• only works if immunization rates in a community are high
  
• e.g. diphtheria, pertussis
  

There is an interesting animation about herd immunity. You guys may want to check it out.

http://www.immunisation.nhs.uk/About_Immunisation/Science/Herd_immunity_-_animation