Phagocytosis (AQA A Level Biology): Revision Note

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

1. Chemotaxis – Chemicals from pathogens or damaged body cells (e.g. histamines) attract phagocytes to the infection site

2. Recognition and attachment

   1. Phagocytes detect non-self antigens on pathogens using receptor proteins on their membrane

   2. Receptors bind to antigens on the pathogen’s surface

3. Engulfment – The phagocyte’s membrane extends around the pathogen, forming a phagocytic vacuole (this is an example of endocytosis)

4. Phagosome formation – The vacuole containing the pathogen is now called a phagosome

5. Phagolysosome formation – The phagosome fuses with a lysosome, forming a phagolysosome

6. Digestion – Lysozymes (digestive enzymes) are released to hydrolyse the pathogen (e.g. breaking down bacterial cell walls)

7. Antigen presentation – In macrophages, digested pathogen fragments may be displayed on the cell surface to activate the specific immune response

During phagocytosis pathogens are engulfed and digested by phagocytes