Phagocytes and antigens
Introduced| English | Meaning |
|---|---|
| immune system/ɪˈmjuːn ˈsɪstəm/ | The cells, tissues and processes that defend an organism against pathogens and other harmful or foreign material. |
| phagocyte/ˈfæɡəsaɪt/ | Immune cells that engulf and digest pathogens or other particles. |
| macrophage/ˈmækrəfɪdʒ/ | An immune cell that engulfs material such as microbes and dead cells and helps coordinate immune responses. |
| antigen/ˈæntɪdʒen/ | A molecule or molecular feature recognised by the immune system that can trigger a specific immune response. |
| phagocytosis/ˌfæɡəsɪˈtəʊsɪs/ | The engulfing and digestion of pathogens by white blood cells. |
| histamine/ˈhɪstəmiːn/ | histamine |
| inflammation/ɪnflæˈmeɪʃn/ | inflammation |
The first line of defence
- Your immune system 免疫系统 is the set of cells that defends against pathogens.
- The first to act are phagocytes 吞噬细胞 — white blood cells like macrophages 巨噬细胞 and neutrophils.
- They recognise what is foreign by its antigens 抗原.
A phagocyte engulfs and digests a pathogen in a process called ______.
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Phagocytosis is part of the first line of internal defence — fast and non-specific.
Phagocytosis 吞噬作用
- A phagocyte destroys a pathogen by phagocytosis:
- it surrounds the pathogen and takes it inside in a vesicle.
- it digests the pathogen with enzymes.
- a macrophage then displays the pathogen's antigen on its surface, to alert other immune cells.
A phagocyte engulfs, digests and displays the pathogen's antigen
Phagocytosis
Step through how a phagocyte deals with a pathogen — engulf it, digest it, then display its antigen to call in the rest of the immune system.
Phagocytes such as macrophages and neutrophils are types of white blood cell.
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Yes — phagocytes are white blood cells; they are the first cells to respond to a pathogen.
In phagocytosis, a phagocyte:
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A phagocyte engulfs the pathogen into a vesicle and digests it with enzymes.
Put the steps of phagocytosis in order.
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Detect → engulf → digest → present the antigen to call in the specific immune response.
After digesting a pathogen, a macrophage:
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The macrophage presents the antigen, which activates the next stage of the immune response.
Antigens: self and non-self
- An antigen is a molecule (usually a protein) on a cell surface that the immune system can recognise.
- Self antigens are the body's own markers — the immune system ignores them.
- Non-self antigens are foreign (e.g. on a pathogen) — these trigger an immune response.
A coloured electron micrograph of a neutrophil (a phagocyte, yellow) engulfing anthrax bacteria (orange)
Non-self antigens trigger an immune response because they:
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Self antigens are ignored; non-self (foreign) antigens are recognised and trigger a response.
Raising the alarm
- Damaged cells and pathogens release signals (such as histamine 组胺) that trigger inflammation 炎症.
- Increased blood flow brings more phagocytes to the site, speeding up the response.
You've got it
- phagocytes (macrophages, neutrophils) are the first defence
- phagocytosis: engulf → digest with enzymes → display the antigen
- an antigen is a surface molecule the immune system recognises
- self antigens are ignored; non-self (foreign) antigens trigger a response