Effect of a single coding polymorphism in the PRNP gene on PrPˢᶜ levels in prion‐infected sheep lymphoid tissues

Sheep orally infected with bovine spongiform encephalopathy (BSE) have been employed as a model for analysing the risk of transmission of variant Creutzfeldt‐Jakob disease by blood transfusion. Previously, our group has shown that the probability of BSE transmission (via blood transfusion) correlates with the PRNP codon 141 genotypes in donor sheep. Since the lymphoreticular system has been established as an important site for disease‐related PrPSc replication, we speculated that the titre of infectivity in the blood depends on the codon 141 genotype and/or levels of PrPSc in the lymphoid tissues. Since PrPSc is often employed as one of the markers for TSEs infectivity, the purpose of this project was to measure and compare PrPSc levels in lymphoid tissues from sheep with different PRNP codon 141 genotypes. ELISA (TeSeETM sheep/goat kit) was adapted to quantify PrPSc in the brain and lymphoid tissues by using truncated recombinant ovine A136R154Q171 PrP as a standard to estimate relative PrPSc level. In the spleen and prescapular lymph nodes, PrPSc concentrations were similar for LL141 and FF141 sheep, but in LF141 sheep were consistently observed below the TeSeE sheep/goat kit cut‐off value (< 2.4ng/mg), suggesting that there is substantially reduced PrPSc deposition in lymphoid tissues. This finding showed codon 141 genotype has no distinct impact on PrPSc deposition in the brain regardless of genotype. The finding indicated that the amount of PrPSc deposited in lymphoid tissues is related to codon 141 genotypes. The effect of genotype on PrPSc deposition will be correlated to the bioassay infectivity through seeding rate determined from an in vitro conversion method (real‐time quaking‐induced conversion assay, RT‐QuIC)