Mechanism involved in phagocytosis:
- Recognition by phagocytic receptor: Mannose receptors, scavenger receptors and receptors for various opsonins bind and ingest microbes, therefore the mannose receptor recognizes microbes and not host cells. The efficacy of phagocytosis is greatly enhanced when microbes are opsonized by specific proteins for which the phagocytes express high affinity receptors
- Engulfment: After a particles is bound to phagocyte receptors, extensions of the cytoplasm flow around it, and the plasma membrane pinches off to form a cytosolic vesicle that enclose the particle.
- Killing and degradation of engulfed material: The killing of microbes and the destruction of ingested materials are accomplished by reactive oxygen species, reactive nitrogen species, mainly derived from nitric oxide, and lysosomal enzymes. This is the final step in the elimination of infectious agents and necrotic cells. The killing and degradation of microbes and elimination of dead-cell debris within neutrophils and macrophages occur most efficiently after their activation. All these killing mechanisms are normally sequestered in lysosomes, to which phagocytosed materials are brought. Thus, potentially harmful substances are segregated from the cell’s cytoplasm and nucleus to avoid damage to the phagocyte while it is performing its normal function.
