phagosome maturation

Definition

Target type: biologicalprocess

A process that is carried out at the cellular level which results in the arrangement of constituent parts of a phagosome within a cell. Phagosome maturation begins with endocytosis and formation of the early phagosome and ends with the formation of the hybrid organelle, the phagolysosome. [GOC:kmv, GOC:tb]

Phagosome maturation is a complex and tightly regulated process that begins with the engulfment of a particle by a phagocyte. The phagosome, a membrane-bound vesicle containing the ingested particle, undergoes a series of transformations as it travels through the cytoplasm, ultimately fusing with lysosomes to degrade the particle. Here's a detailed breakdown of the process:

1. **Particle Recognition and Engulfment:**
- Phagocytes recognize and bind to the particle through various receptors, including Fc receptors for antibody-coated particles, complement receptors for complement-coated particles, and scavenger receptors for a wide range of molecules.
- Actin polymerization drives the extension of pseudopodia that engulf the particle, forming the phagosome.

2. **Phagosome-Lysosome Fusion:**
- Once formed, the phagosome undergoes a series of maturation steps, moving through the cytoplasm and acquiring specific proteins and lipids from different cellular compartments.
- Rab GTPases play a crucial role in this process, guiding the phagosome to the correct location and facilitating its fusion with other organelles.
- A key step is the fusion of the phagosome with early endosomes, which deliver acid hydrolases, a class of degradative enzymes.
- The phagosome then fuses with late endosomes, which further acidify its lumen and contribute additional degradative enzymes.
- Finally, the phagosome fuses with lysosomes, the primary degradative organelles of the cell.

3. **Acidification and Degradative Enzyme Activity:**
- As the phagosome matures, its lumen becomes increasingly acidic due to the action of proton pumps.
- This acidic environment activates the degradative enzymes, including hydrolases and proteases, which break down the engulfed particle into smaller components.

4. **Reactive Oxygen Species (ROS) Production:**
- Phagocytes produce reactive oxygen species (ROS) like superoxide radicals and hydrogen peroxide within the phagosome.
- ROS contribute to the killing of pathogens and the breakdown of ingested particles.

5. **Exocytosis of Residual Bodies:**
- Once the particle has been fully degraded, the phagosome remnants, known as residual bodies, are expelled from the cell via exocytosis.

The precise mechanisms and timing of phagosome maturation vary depending on the type of phagocyte, the nature of the ingested particle, and the environmental conditions. However, the overall process is highly conserved and essential for the proper functioning of the immune system, enabling the clearance of pathogens, cellular debris, and other foreign materials from the body.'
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Proteins (2)

Compounds (7)