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If pathogens manage to bypass the body's non-specific defences (skin, mucus, cilia, stomach acid), the immune system takes over. This lesson covers the three main ways that white blood cells defend the body — a core topic in the AQA GCSE Combined Science Trilogy specification (8464).
White blood cells (also called leukocytes) are produced in the bone marrow and circulate in the blood and lymph. They are part of the body's specific immune response — they can recognise and target particular pathogens.
Every pathogen has unique molecules on its surface called antigens. White blood cells can detect these foreign antigens and mount a targeted response.
| Term | Definition |
|---|---|
| Antigen | A unique protein on the surface of a pathogen (or on a cell) that can trigger an immune response |
| Antibody | A Y-shaped protein produced by white blood cells that is complementary to a specific antigen |
| Toxin | A poisonous substance produced by a pathogen |
| Antitoxin | A substance produced by white blood cells that neutralises toxins |
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