Page 138 - Veterinary Immunology, 10th Edition

Many cell surface proteins bind cells together, but the most
VetBooks.ir important of these are the integrins. Integrins consists of paired

protein chains (heterodimers) that use a unique α-chain paired with
a common β-chain. For example, three β -integrins are found on
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neutrophils. Their α-chain, called CD11a, b, or c, is associated with
common β -chain called CD18. Therefore these three integrins are
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CD11a/CD18 (LFA-1), CD11b/CD18, and CD11c/CD18. As
described previously, LFA-1 on activated neutrophils binds to
ICAM-1 on capillary endothelial cells. CD11b/CD18 also binds

leukocytes to endothelial cells and acts as a complement receptor
(complement receptor 3, CR3) (Chapter 4).

Emigration and Swarming

After binding to blood vessel walls, neutrophils swarm into the
surrounding tissues under the influence of chemokines, lipids, and
other chemoattractants (Fig. 5.8). Most migrating neutrophils
squeeze between the endothelial cells, but about 20% actually pass
through these cells and produce proteases to get through the

basement membrane. They then crawl toward any invading
microbes becoming activated in the process. Since neutrophils are
the most mobile of all the blood leukocytes (they can move at up to

12 µm/min), they are the first to arrive at damaged tissues. The first
cells to arrive sense short-range chemotactic factors. Some of these
neutrophils die and release more chemoattractants. The newly
arrived cells in turn synthesize leukotriene B that is even more
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attractive. Within hours neutrophil swarms gather in enormous
numbers. Under some conditions the numbers of neutrophils in
these swarms may be sufficient to generate pus. This whitish-

yellow liquid consists of accumulated dead neutrophils and tissue
debris. It is produced in especially large amounts in the presence of
bacteria that produce leukotoxins—toxins that kill leukocytes. Such
bacteria are said to be pyogenic (Chapter 26).

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