B Cells and Platelets Harbor Prion Infectivity in the Blood of Deer Infected with Chronic Wasting Disease

Abstract

Substantial evidence for prion transmission via blood transfusion exists for many transmissible spongiform encephalopathy (TSE) diseases. Determining which cell phenotype(s) is responsible for trafficking infectivity has important implications for our understanding of the dissemination of prions, as well as their detection and elimination from blood products. We used bioassay studies of native white-tailed deer and transgenic cer- Chronic wasting disease (CWD) is an infectious proteinmisfolding disease, or transmissible spongiform encephalopathy (TSE), affecting cervids in North America (59, 76-79) and one Asian country (41,68). CWD is unique among prion diseases in affecting free-ranging wildlife populations (deer, elk, and moose). Early and subsequent observations made by Williams and Miller (58,79) related CWD transmission to direct contact with clinically affected deer, as well as indirect contact with environments previously populated by infected deer (57). Bioassay studies of white-tailed deer have demonstrated that body fluids and excreta (saliva, urine, feces, and blood) contain infectious prions (53, 54). Both clinical and preclinical CWDinfected deer harbored sufficient infectious prions to produce CWD in naïve white-tailed deer following ingestion of saliva or transfusion of whole blood (53, 54).The detection of blood-borne infectious prions has important implications for our understanding of the spread of prions among and within individuals, as well as for the elimination of prions from blood products (13,15,33,45), given the evidence for Creutzfeldt-Jakob disease (CJD) transmission via blood transfusion (16,29,47,50,62,72,73). Identifying the cell phenotype or cell-free protein fractions that harbor prion infectivity would contribute importantly to this understanding and to the development of blood-based assays to detect prion infection. We undertook the present studies to address these issues. MATERIALS AND METHODSBioassay studies of white-tailed deer. White-tailed deer fawns were provided by the Warnell School of Forestry and Natural Resources, University of Georgia, Athens-a region in which CWD has not been detected. The deer fawns were hand raised and human and indoor adapted before overnight transport directly to the Colorado State University (CSU) CWD research indoor isolation facility without contact with the native Colorado environment. The 4-month-old fawns were adapted to the facility housing conditions and diet for 2 months before the study start.Genotyping. All white-tailed deer were genotyped to determine their GG/GS (codon 96) status by the laboratory of Katherine O'Rourke, USDA-ARS, Pullman, WA. Deer were allocated into inoculation cohorts (n ϭ 4) without knowledge of their G96 genotypes.Biocontainment protocols. Protocols to preclude extraneous exposure and cross contamination between cohorts of animals as previously described (53, 54) incorporated protective shower-in requirements, Tyvek clothing, masks, head covers, and footwear while maintaining stringent husbandry. Tonsil biopsy ...

Prion transmission

“…Several studies have demonstrated that prions are present in the blood of sheep infected with scrapie and BSE, 16,17 deer incubating CWD, 18,19 and within the blood of patients with preclinical vCJD. 20 Where prion disease does result in widespread tissue distribution of infectious agent, it is likely that mucosal tissues, skin and secretory organs will contain prion.…”

Bioassay of prion-infected blood plasma in PrP transgenic Drosophila

“…Blood plasma from prion-infected hosts is notorious for its poor transmission in conventional prion infectivity bioassays using sentient experimental animals [19,21] and does not act as a seed for the initiation of in vitro PMCA [40]. Furthermore, plasma from scrapie-affected sheep was less efficient than either whole blood or white blood cells in transmission of the disease when recipient scrapie-free sheep were inoculated with these samples by the intravenous route [19].…”

“…Our studies here support the view that the level of prion infectivity in blood from prion-diseased individuals may be underestimated when assessed by intracerebral inoculation of rodents in comparison with bioassay of similar material in other experimental systems. This is particularly pertinent to our assessment here of prion-infected plasma that could be diluted by several orders of magnitude and still trigger a phenotypic response in the PrP transgenic Drosophila, but appears to contain a low level of infectivity when assayed in other systems [10,[15][16][17][18][19][20][21]. One possibility for the efficient detection of scrapie-infected sheep plasma by PrP transgenic Drosophila is that this invertebrate host does not normally express PrP and may therefore not have evolved suitable defence mechanisms that efficiently remove or sequester misfolded neurotoxic forms of this protein.…”

“…Collectively, these studies revealed that prion infectivity titres of blood samples harvested during the asymptomatic phase of prion disease were up to 10-fold less than those collected during the clinical phase [10,19,20,22]. Infectious prions were found to be associated with white and red blood cells, platelets and plasma, although interspecies variations existed with regard to the distribution of prion infectivity in these different blood fractions [10,[15][16][17][18][19][20][21]. Studies in ruminants have analysed bioassays of autologous whole or fractionated blood by the intravenous route [19,20].…”

“…The bioassay of blood-borne prion infectivity has been performed for a variety of different species, such as rodents, sheep, cervids and primates including humans, undergoing, collectively, either experimental or natural prion disease [10,[15][16][17][18][19][20][21]. These bioassays have typically involved intracerebral inoculation of blood, or blood fractions, into a recipient indicator species, usually rodents including mice with a PrP transgene autologous for the donor species.…”