Page 147 - Veterinary Immunology, 10th Edition

Neutrophils kill ingested bacteria through two distinct processes.
VetBooks.ir One involves the generation of potent oxidants by a respiratory

burst. The other involves release of lytic enzymes and antimicrobial
peptides from intracellular granules (Box 5.1).

Box 5.1

Autophagy

Phagocytosis, as described in this chapter, involves the ingestion,
killing, and digestion of extracellular particles such as invading

bacteria. Cells can also destroy particles within the cytosol by
autophagy (see Fig. 5.16). Autophagy is a form of cellular waste
disposal. The structure to be destroyed, such as an intracellular

microbe or a damaged cytoplasmic organelle, is first enclosed
within a double membrane to form a cytosolic vesicle called an
autophagosome. This then fuses with lysosomes, whose enzymes
digest the contents of the autophagosome. Their macromolecules
are then released back into the cytosol, where they can be recycled.

Autophagy can be triggered by starvation to provide more amino
acids for protein synthesis, but it can also be used to selectively
remove organelles such as mitochondria, misfolded and

aggregated proteins, and intracellular infectious agents. Thus TLR7
or FcγR signaling from phagosomes can initiate their targeting by
the autophagy system, possibly by acting through the NOX
complex. Autophagy plays important roles in elimination of
intracellular pathogens, activation of intracellular pattern-

recognition receptors, regulation of inflammasome activation, and
intracellular antigen processing. Disorders of autophagy are
associated with cancer, neurodegeneration, microbial infections,

and aging.

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