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Flashcards in Chapter 9 Deck (19):

What are prions?

An infectious host-derived glycoprotein composed purely of protein (proteinaceous), lacking nucleic acid.
Common in humans and animals. Species specific (except for vCJD)
Resistant to heat, disinfectants and irradiation.


What diseases do prions cause?

Scrapie (sheep), BSE (cattle), Chronic wasting disease (elk) and Kuru or Creutzfeldt-Jakob disease (humans)


What is the pathology of prions?

Large vacuoles in the CNS (spongy brain), causing motor disturbances
Neurodegenerative disease


What is the speed of vCJD?

1-35 years between infection and symptoms


What is vCJD?

Variant of Creutzfeldt-Jakob disease. A prion that jumped from animals to humans. Only interspecies prion.


What is the cause behind prions?

PrP, a host encoded glycoprotein expressed mainly on the surface of nerve cells.
Two types


What is PrPc?

An uninfective glycoprotein with alpha-helical conformation. Susceptible to protease.
Exist at cell membrane as linear proteins.


What is PrPsc?

An infective glycoprotein with beta-sheet conformation. Protease resistant, causing accumulation.
Exist as a free globular glycoprotein, which can interact with PrPc.


How do our good prion proteins become bad ones?

PrPsc interacts with and releases PrPc and from the membrane. It is converted to PrPsc. The cells produce more PrPc and the cycle is repeated. PrPsc accumulates as plaques and is internalized by cells.


What diseases are similar to prion diseases?

Alzhemiers, ALS and Huntingtons


What diseases can mutation in codon 129 of PrPc in chromosome 20 (spontaneous) cause?

CJD, Gertsmann-Straussler-Scheinker syndrome and fatal familial insomnia


What infective agents (iaterogenic) can cause prion diseases?

Food (beef, cannibalism), medical products (blood, transplants), surgical instruments (strong binding to metal surfaces), possibly mother to fetus


How can prions be shed?

Skin, feces, urine, milk, nasal secretions, saliva and placenta


Why do we believe that many people are genetically resistant to prion diseases?

They are shed so many ways and easily spread but it hasn't infected as many people as it should have. Selection has already happened


Which prion crossed the species boundary?

BSE crossed from cattle to human to become vCJD.


Why are prion diseases difficult to diagnose before symptoms arise?

No culturing, serology. No inflammation.


How could we potentially look for prions?

Design antibodies against the beta-sheet or alpha helix form and look for antigen-antibody interactions.


Where can you get a good prion sample from?

From the tonsillar tissue.


What is the treatment for prions?

Currently only experimental in rodents using polyanionic and tricyclic compounds