Abstract
In pursuit of a tractable bioassay to assess blood prion infectivity, we have generated prion protein (PrP) transgenic Drosophila, which show a neurotoxic phenotype in adulthood after exposure to exogenous prions at the larval stage. Here, we determined the sensitivity of ovine PrP transgenic Drosophila to ovine prion infectivity by exposure of these flies to a dilution series of scrapie-infected sheep brain homogenate. Ovine PrP transgenic Drosophila showed a significant neurotoxic response to dilutions of 10-2 to 10-10 of the original scrapie-infected sheep brain homogenate. Significantly, we determined that this prion-induced neurotoxic response in ovine PrP transgenic Drosophila was transmissible to ovine PrP transgenic mice, which is indicative of authentic mammalian prion detection by these flies. As a consequence, we considered that PrP transgenic Drosophila were sufficiently sensitive to exogenous mammalian prions to be capable of detecting prion infectivity in the blood of scrapie-infected sheep. To test this hypothesis, we exposed ovine PrP transgenic Drosophila to scrapie-infected plasma, a blood fraction notoriously difficult to assess by conventional prion bioassays. Notably, pre-clinical plasma from scrapie-infected sheep induced neurotoxicity in PrP transgenic Drosophila and this effect was more pronounced after exposure to samples collected at the clinical phase of disease. The neurotoxic phenotype in ovine PrP transgenic Drosophila induced by plasma from scrapie-infected sheep was transmissible since head homogenate from these flies caused neurotoxicity in recipient flies during fly-to-fly transmission. Our data show that PrP transgenic Drosophila can be used successfully to bioassay prion infectivity in blood from a prion-diseased mammalian host.
Highlights
Prion diseases are fatal neurodegenerative conditions that affect humans and a variety of other vertebrate species [1]
In our studies reported here, we have tested the ability of prion protein (PrP) transgenic Drosophila to act as a tractable bioassay for the detection of infectious prions in the blood from individuals with prion disease
We have shown that adult ovine PrP transgenic Drosophila exposed, at the larval stage, to scrapie-infected sheep plasma exhibited an accelerated decline in locomotor ability compared with the response seen after exposure to scrapie-free plasma
Summary
Prion diseases are fatal neurodegenerative conditions that affect humans and a variety of other vertebrate species [1]. The occurrence of vCJD prions in human lymphoid tissue, together with the detection of prion infectivity in the blood of animals with asymptomatic experimental prion disease [10,11], raised the possibility for the potential of blood-borne vCJD transmission These concerns were realised with the emergence of cases of vCJD in individuals within the U.K. who had received red blood cell concentrates [12,13,14,15]. Abnormal prion protein was detected in a post-mortem spleen sample from a haemophilic patient who had received purified Factor VIII prepared from plasma batches that included donations from individuals who later developed vCJD [12] These particular cases of vCJD infection collectively provide strong support for the view that this prion disease can be transmitted by blood transfusion. Much attention has focused on understanding the biology of infectious prions in blood through the analysis of prion infectivity and PrPSc within different blood fractions from hosts with prion disease
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