Lower specific infectivity of protease-resistant prion protein generated in cell-free reactions.

Laboratory of Persistent Viral Diseases, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, Hamilton, MT 59840, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.81). 11/2011; 108(48):E1244-53. DOI: 10.1073/pnas.1111255108
Source: PubMed

ABSTRACT Prions are unconventional infectious agents that cause transmissible spongiform encephalopathy (TSE) diseases, or prion diseases. The biochemical nature of the prion infectious agent remains unclear. Previously, using a protein misfolding cyclic amplification (PMCA) reaction, infectivity and disease-associated protease-resistant prion protein (PrPres) were both generated under cell-free conditions, which supported a nonviral hypothesis for the agent. However, these studies lacked comparative quantitation of both infectivity titers and PrPres, which is important both for biological comparison with in vivo-derived infectivity and for excluding contamination to explain the results. Here during four to eight rounds of PMCA, end-point dilution titrations detected a >320-fold increase in infectivity versus that in controls. These results provide strong support for the hypothesis that the agent of prion infectivity is not a virus. PMCA-generated samples caused the same clinical disease and neuropathology with the same rapid incubation period as the input brain-derived scrapie samples, providing no evidence for generation of a new strain in PMCA. However, the ratio of the infectivity titer to the amount of PrPres (specific infectivity) was much lower in PMCA versus brain-derived samples, suggesting the possibility that a substantial portion of PrPres generated in PMCA might be noninfectious.

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