Page 164 - Veterinary Immunology, 10th Edition

neutrophil emigration from blood vessels. The release of HMGB1
VetBooks.ir and other damage-associated molecular patterns (DAMPs) from

damaged tissues stimulates macrophages to produce TNF-α and IL-
6 as well as neutrophil chemotactic chemokines and reactive

oxygen species (ROS).
Exosomes are small cytoplasmic vesicles, about 50 to 100 nm in
diameter, that can transmit signals between cells. They are released
by stimulated macrophages, dendritic cells, and B cells. These

exosomes carry with them a mixture of immunostimulatory and
proinflammatory molecules. They can spread through the
extracellular fluid and interact with nearby cells. Thus exosomes
from macrophages containing ingested bacteria can express

bacterial cell wall components such as glycopeptidolipids and other
pathogen-associated molecular patterns (PAMPs) on their surfaces.
These exosomes can bind to PRRs on nearby neutrophils and
macrophages, triggering the release of TNF-α and iNOS, and

promoting more inflammation.

Phagocytosis

When microbial invasion occurs and inflammation develops, blood
monocytes respond to PAMPs and DAMPs by binding to vascular

endothelial cells in a manner similar to their partners, the
neutrophils. Thus adherence and rolling are triggered by selectin
binding, and the cells are brought to a gradual halt by integrins

binding to ligands on vascular endothelial cells. The monocytes
bind to endothelial cell intracellular adhesion molecule-1 (ICAM-1)
by using their β -integrins and then emigrate into the tissues (and
2
change their name to macrophages). Several hours after neutrophils
have entered an inflammatory site, the macrophages arrive.
Neutrophils can reach targets in damaged tissues within 3 to 4
hours. Macrophages require at least 12 hours. These macrophages

are attracted not only by bacterial products and complement
components such as C5a but also by DAMPs from damaged cells
and tissues. Once neutrophils have emigrated into tissues, they too
attract macrophages. Thus neutrophil granules contain macrophage
chemoattractants such as azurocidin and cathelicidins. Activated

neutrophils and endothelial cells also produce monocyte

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