Page 699 - Veterinary Immunology, 10th Edition

cells produce a cytokine mixture that promotes bone resorption. IL-
VetBooks.ir 17 especially promotes osteoclast activation, while IL-10 and

TGFβ1 are downregulated. IL-1β and IFN-γ from the Th1 cells also
promote osteoclast production and bone resorption. Since both

Treg and Th17 cells are present in inflamed periodontal tissues, it is
believed that an imbalance in these T cell populations, especially a
deficiency in Treg cells, contributes to the chronic inflammatory
process. For example, both IL-17 and IL-35 are expressed in

inflamed periodontal tissue, and it has been demonstrated that if
Treg populations in dogs with experimental periodontal disease
are enhanced, the progress of disease is slowed. The bone
resorption and soft tissue destruction are mediated by host matrix

metalloproteases and collagenases. The matrix metalloproteases
degrade extracellular matrix, especially type I collagen, and
basement membrane components in the periodontal supporting
tissues. Oxidative and proteolytic activation cascades destroy both

tissues and bone and give rise to the gross lesions associated with
periodontal disease.

FIG. 22.5 A section of pig tonsil showing a tonsillar crypt. Note
how thin the epithelium is at the base of the crypt. This is an easy
invasion route for many organisms. Original magnification ×150.
(Courtesy Dr. S. Yamashiro.)

In single-stomached animals, the gastric pH may be sufficiently

low to have an antimicrobial effect, although this varies among

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