Page 91 - Veterinary Immunology, 10th Edition

VetBooks.ir Antimicrobial Molecules

The products of sentinel cells do two things: they increase vascular
permeability and blood flow and at the same time attract white

blood cells (leukocytes) to sites of microbial invasion and/or tissue
damage. These leukocytes initially consist primarily of neutrophils,
but these are followed by a wave of macrophages (Chapter 6). Their
function is to kill microbial invaders as fast and as completely as
possible. To this end, these cells produce a multitude of

antimicrobial molecules.

Peptides

Antimicrobial peptides are widely distributed throughout the plant

and animal kingdoms, and more than 800 have been identified to
date. They include defensins, cathelicidins, C-type lectins, and S100
proteins. Different animal species employ their own specific set of
peptides that have evolved in response to microbial invasion (Box

3.1). Although structurally diverse, these peptides usually contain
multiple arginine and lysine residues, making them cationic, and
they can form amphipathic structures; that is, they have both
hydrophobic and hydrophilic regions. The hydrophobic regions can

bind and insert themselves into the lipid-rich membranes of
bacteria, whereas the other regions form channel-like pores or
simply cover the membrane. This results in bacterial disruption and
death. These cationic antimicrobial peptides kill both Gram-positive

and -negative bacteria as well as some fungi, protozoa, enveloped
viruses, and tumor cells. However, specific defensins may have
different antimicrobial specificities.

Box 3.1

The Big Picture

The complete bovine genome has been sequenced, and
unexpectedly, it was found to contain unusually large numbers of

genes associated with innate immunity. For example, cattle have 10
cathelicidin genes, compared with only 1 in humans and mice.

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