Prions and Prion Diseases

Prions are generally regarded as the most reliable markers of so-called prion diseases. With the advent of the protein-only concept of the transmission of prion diseases, which is predicated on the idea that prions are the infectious agents causing prion disease, and with the 1997 Nobel Prize for Medicine awarded for the prion protein concept, prions have firmly asserted their inclusion in the club of infectious agents, along with bacteria, viruses, fungi, and parasites, the club's traditional members. The essence of the protein-only theory is that the abnormal prion enters the organism and converts the host’s normal prions into abnormal prions. The efficiency of the conversion is influenced by the degree of amino acid sequence homology between the two PrPs involved, so that the greater the degree of homology, the greater the rate of conversion. Several studies suggest that white blood cells may be involved in the process. It was observed that gut-associated macrophages initially remove transmissible spongiform encephalopathy (TSE) infectivity, but once their ability to remove the infectivity completely is overcome, macrophages may facilitate the spread of infectivity. Regulatory measures introduced to prevent the spread of TSEs to humans and other animal species are likely to stay. It is possible, however, that more research and better tests will more adequately characterize risk, which in turn may lead to a gradual loosening of some of the currently existing restrictions following a carefully performed risk assessment.