There are several different types of white blood cells, each with different functions, but they can be put into two main groups:
- phagocytes
- lymphocytes
Phagocytes
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Phagocytes can easily pass through blood vessel walls into the surrounding tissue and move towards pathogens and toxins. They then either:
- ingest and absorb the pathogens or toxins, or
- release an enzyme to destroy them.
Having absorbed a pathogen, the phagocytes may also send out chemical messages that help nearby lymphocytes to identify the type of antibody needed to neutralise them.
In the diagrams below, the grey blobs that look like frog-spawn represent the phagocytes, which deal with the bacteria, represented by small brown rods.
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Lymphocytes
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On the surface of many pathogens are certain chemicals that trigger our immune response. The chemicals are called antigens.
Each lymphocyte carries a specific type of antibody - a protein that has a chemical “fit” to a certain antigen. When a lymphocyte with the appropriate antibody meets the antigen, the lymphocyte reproduces quickly, and makes many copies of the antibody that neutralises the pathogen.
In the diagrams below, the 'crosses' represent bacteria; the orange blobs represent lymphocytes; and the little dark 'spanners' represent antibodies that 'hook' onto and neutralise the bacteria.
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Antibodies neutralise pathogens in a number of ways:
- They bind to the pathogens and damage or destroy them.
- They bind to the pathogens and release chemical signals to attract phagocytes, which then destroy the pathogens.
- They coat pathogens, clumping them together so that they are easily ingested by phagocytes.
[ This page has been adapted from www.bbc.co.uk/schools/gcsebitesize/science
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