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• Mosquito feeding


  1. Lands on arm

  2. Injects chemicals into skin

  3. Begins to feed
• Mosquito bite


  Red lump appears, accompanied by itch
• Immune system


  Body's major safeguard against infection, illness, and disease
• Immune system


  • Vast network of cells, tissues, and organs that coordinate the body's defenses against threats to health
  • Without it, exposed to billions of bacteria, viruses, and toxins that could make minor things fatal
• Leukocytes


  Defensive white blood cells that originate in bone marrow and migrate into bloodstream and lymphatic system
• There are between 4,000 and 11,000 leukocytes in every microliter of blood
• Leukocytes


  Work like security personnel, constantly screening the blood, tissues, and organs for suspicious signs
• Antigens


  Molecular traces on the surface of pathogens and other foreign substances that betray the presence of invaders
• Immune response


  1. Leukocytes detect antigens

  2. Protective immune response kicks in within minutes
• Immune response


  • Has to be equally adaptable as threats are hugely variable
  • Relies on many different types of leukocytes to tackle threats in different ways
• Main cellular groups of leukocytes

  • Phagocytes
  • Lymphocytes
• Phagocytes


  1. Trigger immune response by sending macrophages and dendritic cells into blood

  2. Destroy foreign cells by consuming them

  3. Identify antigen on invaders and transmit information to lymphocytes
• Lymphocytes


  1. T-cells go in search of infected body cells and kill them

  2. B-cells and helper T-cells use antigen information to produce antibodies
• Antibodies


  Special proteins produced by B-cells that can latch onto unique antigens like a lock and key, and destroy invading cells
• Immune response processes


  High temperatures and swelling aid the immune response
• High temperatures


  Make it harder for bacteria and viruses to reproduce and spread because they're temperature-sensitive
• Swelling


  Caused by chemicals released from damaged body cells, which attract phagocytes to consume invaders and damaged cells
• Immune response usually eradicates a threat within a few days
• Immune system's purpose


  To stop a threat from escalating to dangerous levels inside the body, not necessarily to stop you from getting ill
• Immune system's long-term benefit

  Helps develop immunity by allowing B- and T-cells to recognize invaders in the future and deploy the right antibodies
• Diseases immunity can develop to

  • Chickenpox
• Autoimmune diseases


  Trick the immune system into attacking the body's own healthy cells
• Healthy immune system fights off an estimated 300 colds and innumerable other potential infections over a lifetime
• Without the immune system, those threats would escalate into something far more dangerous