More about white blood cells

There are several different types of white blood cells, each with different functions, but they can be put into two main groups:

• phagocytes or macrophages
• lymphocytes

Phagocytes

Phagocytes can easily pass through blood vessel walls into the surrounding tissue and move towards pathogens [pathogens: micro-organisms that cause disease ] or toxins [toxins: a type of natural poison produced by an organism, often as a form of protection ]. They then either:

• ingest and absorb the pathogens or toxins
• 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.

Lymphocytes

Pathogens contain certain chemicals that are foreign to the body and 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.

Antibodies neutralise pathogens in a number of ways:

• they bind to pathogens and damage or destroy them
• they coat pathogens, clumping them together so that they are easily ingested by phagocytes
• they bind to the pathogens and release chemical signals to attract more phagocytes

Lymphocytes may also release antitoxins that stick to the appropriate toxin and stop it damaging the body.