Non-Specific Defences - Phagocytosis

What are phagocytes?

Specialised white blood cells that engulf and destroy pathogens

What are the 2 types of phagocytes?

Neutrophils and macrophages

Difference between neutrophils and macrophages

• Neutrophils have multi-lobed nuclei, which makes it easier for them to squeeze through small gaps to get to the site of infections. It also has granular cytoplasm, containing many lysosomes that contain enzymes used to attack pathogens.

• Macrophages have simpler round nuclei

Phagocytosis Process

1. Pathogens produce chemicals that attract phagocytes

2. Pathogen is engulfed and phagosome is formed

3. Lysosome fuse with the phagosome to form a phagolysosome

4. Hydrolytic enzymes in the phagolysosome break down (hydrolyse) the pathogen

5. Harmless products like the amino acids are absorbed into the cytoplasm

6. The digested pathogen combines with MHC in the cytoplasm. The MHC-antigen complex is displayed on phagocyte membrane, making an antigen presenting cell (APC)

What are cytokines?

Released from T helper cells to trigger clonal expansion of B cells

What are opsonins?

Opsonins are molecules that bind to antigens on the surface of pathogens, making them easier for phagocytes to recognize and engulf, thereby increasing the rate of phagocytosis

Neutrophil Structure

• Multi-lobed nuclei, which makes it easier for them to squeeze through small gaps to get to the site of infections.

• Granular cytoplasm, containing many lysosomes that contain enzymes used to attack pathogens.

Lymphocyte Structure

Spherical nucleus

Monocyte Structure

Unilobular nuclei (kidney shaped - different to neutrophil)

Erythrocyte Structure (red blood cell)

Biconcave disc