Phagocytosis (AQA A Level Biology)

Phagocytosis

• Phagocytes are white blood cells that are produced continuously in the bone marrow

• There are two main types of phagocyte, each with a specific mode of action:

  • neutrophils

  • macrophages

• The role of phagocytes is to recognise and engulf pathogens; this process is known as phagocytosis

• Phagocytosis is an example of a non-specific immune response

The process of phagocytosis

• Chemicals released by pathogens, as well as chemicals released by body cells under attack, e.g. histamines, attract phagocytes

  • This response to chemical stimuli is known as chemotaxis

• Phagocytes move towards the site of infection, where pathogens can be identified due to the presence of pathogenic antigens

  • Phagocytes have receptor proteins on their surface that recognise antigens as non-self

• The phagocyte attaches to the pathogen by binding to its antigens

• Once attached to a pathogen the cell surface membrane of the phagocyte extends out and around the pathogen, engulfing it and trapping the pathogen within a phagocytic vacuole

  • This part of the process is known as endocytosis

  • The phagocytic vacuole formed around a pathogen once it has been engulfed by a neutrophil is called a phagosome

• The phagocytic vacuole fuses with a lysosome to form a phagolysosome

• The lysosome releases digestive enzymes called lysozymes to digest the pathogen, e.g. by hydrolysis of bacterial cell walls

• The products of pathogen digestion can sometimes be displayed on the cell surface of the phagocyte (this occurs in macrophages) to trigger the specific immune response

During phagocytosis pathogens are engulfed and digested by phagocytes