Page 214 - Veterinary Immunology, 10th Edition

are deposited in the neurons of patients with Alzheimer's disease.
VetBooks.ir prion proteins that cause the spongiform encephalopathies such as
Misfolded proteins may be transmissible (Box 7.3). They form the

bovine spongiform encephalopathy (BSE) and scrapie. Prions are

protease-resistant forms of cellular proteins. In the case of BSE, the
prion is a misfolded and aggregated form of a cellular protein PrP c
that is important for normal macrophage functions. These proteins
normally play a role in resistance to intracellular bacteria such as

Brucella. It is also of interest to note that even reactive amyloidosis
is somewhat “transmissible” since inoculation of AA proteins into
an animal will hasten the development of amyloidosis. In such
cases, amyloid proteins likely act by providing a substrate on which

other misfolded proteins can be deposited. There is evidence that
foie gras prepared from duck or goose liver can transmit AA
amyloidosis when fed to mice. Similarly, silk fibers formed from a
protein composed of β-sheets, may promote amyloidosis when

inserted into mice!

Box 7.3

Transmissible Amyloidosis?

AA amyloidosis is unusually common in captive cheetahs and
poses a significant threat to the species' survival. Upon
investigation, however, it was found that cheetahs suffering from
amyloidosis excreted AA amyloid fibrils in their feces. These fecal
amyloid fibers could be purified and injected into mice, where they

were much more effective than tissue amyloid in inducing
amyloidosis. Thus cheetahs appear to transmit AA amyloid in their
feces. This material may cause disease in mice that happen to

ingest cheetah feces. It is also possible that amyloidosis may
develop in cheetahs that happen to eat these mice! It may also be
that other cheetahs may acquire the amyloidosis by fecal
contamination of cuts or abrasions. Given that cheetahs are
genetically homogeneous and tend to suffer from many chronic

inflammatory diseases, they may be more susceptible to
amyloidosis than other species. The transferred amyloid might
simply enhance an ongoing disease. Thus AA amyloidosis in

cheetahs may be a prion disease.

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