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Immunity

We all live with millions of harmless microbes in and on our bodies. But a few dangerous microbes can cause diseases when they enter our bodies.

Immune response sequence

Bacteria covered in antigens

Picture 16. A pathogen has antigens on its surface.

All cells, including microbes, have particular proteins on their surfaces which act as markers. These are called antigens. If microbes get into the body they trigger a reaction by the immune system. The immune system recognises that the protein markers on a microbe are foreign to the body. This tells the body’s white blood cells to produce antibodies. The antibodies coat the microbes and make them clump together. That makes it easier for white blood cells to surround and kill them.

You can find out more about immune response in The human immune system.

Picture 17. How vaccination protects us against pathogens.
Open the animation in a new window.

Lasting immunity

After an infection, some white blood cells act as an immune ‘memory’. If the same type of microbe infects the body a second time, the white blood cells can respond more quickly and produce the same antibodies as last time.

This immune ‘memory’ can be used to prevent infection and disease by immunisation.

A person is immunised by injecting them with some antigen or dead pathogen. This triggers the immune response without causing a serious infection. However, the immune memory means that the white blood cells are ready to attack the real disease quickly if and when it infects the person.