Page 94 - Veterinary Immunology, 10th Edition

In addition to their antibacterial functions, granulysins attract and
VetBooks.ir activate macrophages. Two other important antibacterial proteins

are bactericidal permeability-increasing protein (BPI) and
calprotectin. BPI is a major constituent of the primary granules of

human and rabbit neutrophils. It kills Gram-negative bacteria by
binding to lipopolysaccharides and damaging their inner
membrane. Calprotectin is found in neutrophils, monocytes,
macrophages, and epidermal cells. It forms about 60% of neutrophil

cytosolic protein and is released in large amounts into blood and
tissue fluid in inflammation. It belongs to the S100 family of
antimicrobial proteins. Calprotectin sequesters zinc and manganese
during bacterial infections and thus makes them unavailable for

bacterial growth.
The production of some antimicrobial proteins by epithelial cells
is regulated by cytokines. In particular, the two cytokines produced
by Th17 cells, IL-17 and IL-22, are crucial regulators of antimicrobial

peptide production in the intestine and lungs (Chapter 22).
Likewise, IL-1 stimulates epithelial cells to produce antimicrobial
proteins. Antimicrobial peptides regulate cytokine production and
can serve as immunomodulators. For example, lactoferrin

stimulates macrophage production of IL-18, whereas some
cathelicidins stimulate production of IL-6, IL-8, and IL-10.

Lysozyme

The enzyme lysozyme cleaves the bond between N-acetyl-
muraminic acid and N-acetylglucosamine and destroys cell wall
peptidoglycans in Gram-positive bacteria. Lysozyme is found in all
body fluids except cerebrospinal fluid and urine. It is present in
large amounts in inflammatory tissue fluid. While absent from

bovine neutrophils and tears, it is present in high concentrations in
the tears of other mammals. Although many of the bacteria killed
by lysozyme are nonpathogenic, it might reasonably be pointed out

that this susceptibility could account for their lack of pathogenicity.
Lysozyme is found in high concentrations in neutrophil granules
and accumulates in areas of acute inflammation, including sites of
bacterial invasion. Lysozyme is also a potent opsonin, binding to
bacterial surfaces and facilitating phagocytosis in the absence of

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