ninja icon


•  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)


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