C3.2.5 Infection control by phagocytes Notes

Infection Control by Phagocytes

1. Imagine you cut your finger while gardening.
2. Within hours, the area becomes red and swollen.
3. This is your immune system springing into action, with phagocytes, specialized white blood cells, leading the charge.
4. Phagocytes are a crucial component of the innate immune system and play a vital role in defending the body against infection.
5. These cells recognize, engulf, and digest pathogens through a process known as phagocytosis.

Amoeboid Movement: How Phagocytes Reach the Battlefront

1. Phagocytes, like macrophages and neutrophils, are not confined to blood vessels. They move to infection sites using amoeboid movement.
2. Amoeboid movement is a crawling-like motion that allows cells to navigate through tissues.
3. The process works as so:
   1. Chemotaxis: Phagocytes detect chemical signals from damaged tissues or pathogens.
   2. Diapedesis: They squeeze through capillary walls into tissues.
   3. Pseudopodia: Extensions of the cell membrane help them move toward the infection.

Recognizing and Engulfing Pathogens

1. Once at the infection site, phagocytes identify pathogens by detecting antigens on their surfaces.
2. Antigens are molecules that trigger an immune response.

Steps of Pathogen Recognition and Engulfment

1. Recognition: Phagocytes bind to antigens using receptors on their surface.
2. Engulfment: The cell membrane wraps around the pathogen, forming a vesicle called a phagosome.
3. Digestion: The phagosome merges with a lysosome, creating a phagolysosome. Enzymes inside the lysosome break down the pathogen.

Digestion by Lysosomal Enzymes

1. The phagosome then fuses with a lysosome, a specialized organelle containing digestive enzymes, forming a phagolysosome.
2. The enzymes within the lysosome, such as lysozyme and proteases, break down the pathogen, digesting it into smaller, harmless components.
3. The phagocyte then expels the indigestible waste material by exocytosis.

The Role of Enzymes in Digestion

Lysosomes contain powerful enzymes like lysozyme and proteases that degrade pathogens.

1. Lysozyme: Breaks down bacterial cell walls.
2. Proteases: Digest proteins into smaller peptides.

Why Is This Process So Effective?

1. Rapid Response: Phagocytes act quickly, often within minutes of infection.
2. Broad Target Range: They can engulf bacteria, fungi, and even dead cells.
3. Signal Amplification: After digesting pathogens, phagocytes release signals to recruit more immune cells.

What Happens After Digestion?

1. After breaking down the pathogen, phagocytes perform two critical tasks:
   1. Waste Removal: Undigested material is expelled from the cell.
   2. Antigen Presentation: Some phagocytes, like macrophages, display pathogen fragments on their surface. This activates the adaptive immune system, which provides long-term protection.

Why Is Phagocytosis Important?

1. Without phagocytosis, even minor infections could become life-threatening.
2. This process is crucial for:
   1. Preventing Infections: By destroying pathogens before they spread.
   2. Cleaning Up Debris: Removing dead cells and waste from tissues.
   3. Activating the Immune System: Initiating the adaptive immune response.