Page 62 - Veterinary Immunology, 10th Edition

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FIG. 2.7 Bacterial lipopolysaccharide cannot bind TLR4 directly. It
must first bind to lipopolysaccharide-binding protein and then to two
other proteins, MD-2 and CD14, before it can bind and activate cells
such as macrophages.

Bacterial Peptidoglycans

Peptidoglycans are polymers of alternating N-acetylglucosamine

and N-acetylmuraminic acid that are major constituents of the cell
walls of both Gram-positive and -negative bacteria. PRRs that can
bind these peptidoglycans include some TLRs, NODs, and CD14.
Peptidoglycan recognition proteins (PGRPs) are PRRs that induce

the production of proinflammatory and antimicrobial peptides.
They are found in humans, mice, cattle, and pigs. In pigs, PGRPs
are expressed constitutively in the skin, bone marrow, intestine,
liver, kidney, and spleen. Bovine PGRP-S can kill microorganisms

in which the peptidoglycan is either buried (Gram-negative
bacteria) or absent (Cryptococcus), raising questions about its precise
ligand. PGRP-S also binds bacterial lipopolysaccharides and
lipoteichoic acids. It is found in neutrophil granules, and these

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