What is phagocytosis?When a macrophage acts as a phagocyte, what events are involved? (Hint: receptor-mediated endocytosis)
Binding of pathogen to phagocytic receptors initiates receptor-mediated endocytosis (phagocytosis). Pathogen becomes enveloped and is turned into a phagosome vesicle, joined by a lysosome-phagosome (phagolysosome) which lysosome contains enzymes and toxic substances to destroy pathogen.
Phagocytosis is a form of endocytosis in which cells engulf solid particles. When a macrophage acts as a phagocyte, the following events are involved:
1. Chemotaxis: The microbe or particle is detected by the macrophage through chemical signals and is attracted towards the site of infection.
2. Recognition: The macrophage identifies the microbe or particle through receptors, most commonly Toll-like receptors (TLRs), which recognize specific molecular patterns on the surface of the invader.
3. Attachment: The macrophage attaches to the microbe or particle through the interaction between the receptors and their ligands.
4. Engulfment: The macrophage extends its plasma membrane around the microbe or particle, forming a phagosome.
5. Fusion: The phagosome fuses with lysosomes within the cytoplasm of the macrophage, forming a phagolysosome.
6. Killing: The microbe or particle is destroyed through a combination of oxidative burst and the action of lysosomal enzymes.
7. Exocytosis: The residual material is released outside of the cell through exocytosis.
Receptor-mediated endocytosis is an important process for phagocytosis, as it allows the macrophage to selectively recognize and engulf targets, which can include bacteria, fungi, viruses, and other foreign particles.
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