Prions (the name is derived from proteinacious infectious particle) is the name used by many scientists to describe the pathogen that causes transmissible spongiform encephalopathies (TSE) which are neurodegenerative diseases in mammals. Prions are a disease-causing form of a normal protein called cellular prion protein (PrPC) that is located primarily on the surface of central nervous system cells but also in other tissues of the body in mammals. The specific function of the normal prion protein (PrPC) is not clearly understood, but in experimental models it appears to play a role in protecting cells and helping them respond to oxygen deficiency.1

Prions are extremely small, smaller than viruses, and even through an electron microscope only aggregations (clusters), not individual prions, can be seen.

Prions are unique pathogens in that they appear to have no nucleic acid and thereby differ from viruses, bacteria, fungi and other pathogens. Prions are resistant to procedures that break down nucleic acid and destroy biological forms of pathogens.

In addition, prions differ from other pathogens in that they are responsible for genetic, sporadic and acquired forms of neurodegenerative disease. Also, because prions are an abnormal form of a normal protein that is genetically encoded, they do not produce an immune response in the host as would a foreign infectious agent.

Lacking nucleic acid, prions cannot reproduce, but they replicate by stimulating normal cellular prion protein to refold into a form called PrP scrapie (PrPSc) – named after scrapie, the first TSE discovered. The conversion of normal prion protein (PrPC) into abnormal prion protein (PrPSc) and replication of prions in the brain causes degeneration of neural tissue and, ultimately, death. The process by which the prion recruits normal prion protein (PrPC) to convert to the disease-causing form remains unknown.

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