Phagocytes and antigens
| English | Chinese | Pinyin |
|---|---|---|
| immune system | 免疫系统 | miǎn yì xì tǒng |
| phagocyte | 吞噬细胞 | tūn shì xì bāo |
| macrophage | 巨噬细胞 | jù shì xì bāo |
| antigen | 抗原 | kàng yuán |
| phagocytosis | 吞噬作用 | tūn shì zuò yòng |
| histamine | 组胺 | zǔ àn |
| inflammation | 炎症 | yán zhèng |
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 ______.
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.
Yes — phagocytes are white blood cells; they are the first cells to respond to a pathogen.
In phagocytosis, a phagocyte:
A phagocyte engulfs the pathogen into a vesicle and digests it with enzymes.
Put the steps of phagocytosis in order.
Detect → engulf → digest → present the antigen to call in the specific immune response.
After digesting a pathogen, a macrophage:
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:
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