How do you recognise invaders?

Your T- and B-cells recognise invaders by the shape of molecules - antigens - on their surfaces. Your immune system can produce a T- and B-cell to fit every possible shape. However, any T- or B-cell that recognised molecules found on your cells were destroyed while you were growing in the womb, to prevent them from attacking your own body. But you were left with millions of others, one for every foreign antigen you might ever encounter.

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Electron micrograph of Escherichia coli, close-up.

What is so special about your T-cells?

Having recognised the invader, different types of T-cell then have different jobs to do. Some send chemical instructions (cytokines) to the rest of the immune system. Your body can then produce the most effective weapons against the invaders, which may be bacteria, viruses or parasites. Other types of T-cells recognise and kill virus-infected cells directly. Some help B-cells to make antibodies, which circulate and bind to antigens.

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A T-cell (orange) killing a cancer cell (mauve).

What is so special about your B-cells?

With the help of T-cells, B-cells make special Y-shaped proteins called antibodies. Antibodies stick to antigens on the surface of germs, stopping them in their tracks, creating clumps that alert your body to the presence of intruders. Your body then starts to make toxic substances to fight them. Patrolling defender cells called phagocytes engulf and destroy antibody-covered intruders.

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The molecular structure of an antibody.

 

Principal Funder:

Wellcome trust

Major Sponsors:

GlaxoSmithKline life technologies