Sheep With the Homozygous Lysine-171 Prion Protein Genotype Are Resistant to Classical Scrapie After Experimental Oronasal Inoculation

Abstract

Scrapie is a fatal neurodegenerative disease of sheep resulting from the accumulation of a misfolded form of the prion protein (PrPSc). Polymorphisms in the host prion protein gene ( PRNP) can affect susceptibility to the scrapie agent. Lysine (K) at codon 171 of PRNP is an inadequately characterized, naturally occurring polymorphism in sheep. We inoculated Barbado sheep with PRNP genotypes QQ171, QK171, or KK171 by either the intracranial (IC, n = 2–7 per genotype) or oronasal (ON, n = 5 per genotype) routes with a scrapie isolate to investigate the effect of lysine at codon 171 on susceptibility. When neurologic signs were observed or at the end of the experiment (70 months postinoculation [MPI]), sheep were necropsied and tissue collected for histopathologic, immunohistochemical, enzyme immunoassay and Western blot examination for PrPSc. All genotypes of sheep developed scrapie after IC inoculation. After ON inoculation, sheep with the QK171 genotype had prolonged incubation periods compared to the QQ genotype. During the experiment, 2 of 5 of the ON-inoculated QK genotype sheep developed neurologic signs and had PrPSc in the brain. The other 3 of 5 sheep were asymptomatic at 70 MPI but had detectable PrPSc in peripheral tissues. None of the ON-inoculated sheep of the KK171 genotype developed signs or had detectable PrPSc. Our experiments demonstrate that sheep with the KK171 genotype are resistant to scrapie via oronasal exposure and that sheep with the QK171 genotype have prolonged incubation relative to QQ171 sheep. The K171 prion protein allele may be useful to enhance scrapie resistance in certain breeds of sheep.

Experimental inoculation of CD11c+ B1 lymphocytes, CD68+ macrophages, or platelet-rich plasma from scrapie-infected sheep into susceptible sheep results in variable infectivity

“…Specifically, sheep with the ARQ/ ARQ genotype had more PrP Sc in the grey matter than the white matter (most evident at the level of the basal nuclei), while sheep with the VRQ/ARQ genotype had similar levels of PrP Sc in the white and grey matter. The finding of genotypeassociated differences in the accumulation of PrP Sc in the grey and white matter of recipient sheep after intracranial inoculation has been observed previously [67]. In order to determine whether the disease phenotype was influenced by inoculum cell type, or host versus recipient genotypes, we constructed immunohistochemical PrP Sc profiles.…”

Sheep Are Susceptible to the Bovine Adapted Transmissible Mink Encephalopathy Agent by Intracranial Inoculation and Have Evidence of Infectivity in Lymphoid Tissues

“…The number of sheep for each genotype inoculated intracranially was VRQ/VRQ, n = 5; VRQ/ARQ, n = 4; ARQ/ARQ, n = 4; and ARQ/ARR, n = 4. The procedure for intracranial inoculation was performed as previously described (20–22) using 1 ml of brain homogenate. Oronasal inoculation also was performed as previously described and demonstrated to be effective for the transmission of the scrapie agent (23, 24).…”

“…The procedure for collection of samples was performed similar to other experiments (22). At necropsy, duplicate tissue samples were collected and stored in 10% buffered neutral formalin (globes in Bouin's fixative) or frozen.…”

Bovine adapted transmissible mink encephalopathy is similar to L-BSE after passage through sheep with the VRQ/VRQ genotype but not VRQ/ARQ

“…Enzyme immunoassay (EIA) was carried out similarly to previously described methods [12,54] using a commercially available enzyme-linked immunoassay (HerdChek®, IDEXX Laboratories Inc., Westbrook, ME). Frozen brain samples were prepared as a 20% (w/v) tissue homogenates and treated with proteinase K. From that point, the assay was completed according to kit instructions.…”