• Large particles (like those of bacteria) can be engulfed through the process of phagocytosis. The white blood cells which carry out this process are the Phagocytes (Macrophages).
  • Phagocytosis is a non-specific immunity as it simply engulfs pathogens, not caring what they are.

  • Phagocytes travel in the blood but can move out of the blood vessels into other tissues
  • Chemical products of pathogens, dead or damaged cells or abnormal cells act as attractants causing phagocytes to move towards these pathogens. (chemotaxis)
  • Phagocytes have several receptors on their cell surface membrane that recognise and attach to chemicals on the surface of the pathogen.
  • They engulf the pathogen to form a vesicle, known as a phagosome
  • Lysosomes moves towards the vesicle and fuse with it
  • Enzymes called Lysozymes are present within the lysosome. These lysozymes destroy ingested bacteria by hydrolysis of their cell walls. The process is the same as that for digestion of food in the intestine, namely the hydrolysis of larger, insoluble molecules into smaller soluble ones
  • The soluble products from the breakdown of the pathogen are absorbed into the cytoplasm of the phagocyte
  • The phagocyte also presents the antigens of the pathogen it has for the T-cells for their specific response