Background: What is the immune system?

Links to activities: comic strip, Professor Helix videos, and vaccinations activity.

Immunity is the body’s ability to protect itself from infections. Our body is extremely efficient at keeping us healthy and has multiple lines of defence that limit infections caused by harmful microbes.

Harmful microbes can be kept out of the body. Some examples include:

  • The skin stops microbes entering the body.
  • The nose has a sticky membrane to trap microbes if they are inhaled.
  • The tears contain substances which kill bacteria.
  • The stomach produces acid which can kill many microbes.

Cartoon image of body with tears, skin, and gastric acid labelled to show the primary defences in the body

Image taken from ‘Types of Immunity’.

Non-specific White Blood Cells (WBC) circulate in the body and attack anything that it considers foreign to the body.

  • These WBCs are known as phagocytes and are non-specific because they will try to engulf and digest any foreign bodies by a process known as phagocytosis.
  • They also trigger an inflammatory response, helping the right cells to get to the area and fight the infection. This may cause swelling, pain and redness.

Close up (3D computer) image of a white blood cell

Image taken from ‘Types of Immunity’.

Specific WBCs can target harmful microbes within the body and destroy them.

  • These WBCs target specific invading microbes through a unique molecule on the invaders’ surface called an antigen.

  • When they come across an antigen they do not recognise they start to produce antibodies and mark it for destruction by other WBCs.

  • WBCs stay in the blood and quickly produce antibodies ready to fight an invader with this antigen, should it return. In this way, the body maintains a memory of the disease, making us immune to many diseases we have already had.

In healthy people, the body’s defences can usually prevent or fight off infection caused by harmful microbes (pathogens or germs).

Medical professionals may suggest ways we can help boost our body’s defences or, in some cases, prescribe treatments that work to directly destroy them, like antibiotics.

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