Page 148 - Veterinary Immunology, 10th Edition

VetBooks.ir

FIG. 5.16 The process of autophagy, a method of cellular waste
disposal. An autophagosome forms within the cytoplasm and
encloses the organelle or microbe to be destroyed. Lysosomes fuse
with the autophagosome to form an autolysosome. The contents
are degraded and recycled. This is a way to get rid of old, damaged
organelles as well as intracellular bacteria.

The Respiratory Burst

Within seconds after binding a bacterium, neutrophils increase their
oxygen consumption nearly 100-fold by activating a cell surface
enzyme complex called NADPH oxidase (NOX). The NOX
components are separate in resting cells, but when a neutrophil

encounters TNF or is exposed to other inflammatory stimuli, they
assemble to form a complete complex (Fig. 5.14). Activated NOX
converts NADPH (the reduced form of NADP, nicotinamide
+
adenine dinucleotide phosphate) to NADP with the release of
electrons. A molecule of oxygen accepts a donated electron,
•
−
generating a superoxide anion (the dot in O denotes the presence
2

148