Understanding:
• Ingestion of pathogens by phagocytic white blood cells gives non-specific immunity to disease
The second line of defence against infectious disease is the innate immune system, which is non-specific in its response
- A principle component of this line of defence are phagocytic white blood cells that engulf and digest foreign bodies
- Other components of the innate immune system include inflammation, fever and antimicrobial chemicals (complement proteins)
The innate immune system has two key properties:
- It does not differentiate between different types of pathogens (non-specific)
- It responds to an infection the same way every time (non-adaptive)
Phagocytes
Phagocytosis is the process by which solid materials (such as pathogens) are ingested by a cell (i.e. cell ‘eating’ via endocytosis)
- Phagocytic leukocytes circulate in the blood and move into the body tissue (extravasation) in response to infection
- Damaged tissues release chemicals (e.g. histamine) which draw white blood cells to the site of infection (via chemotaxis)
- Pathogens are engulfed when cellular extensions (pseudopodia) surround the pathogen and then fuse to form an internal vesicle
- The vesicle is then fused to a lysosome (forming a phagolysosome) and the pathogen is digested
- Pathogen fragments (antigens) may be presented on the surface of the phagocyte in order to stimulate the third line of defence
Phagocytosis by Leukocytes
