Background and objectives: Transmissible spongiform encephalopathies (TSEs) including sheep scrapie are characterized by the conversion of a normal, cellular prion protein (PrPc) to an abnormal protease-resistant form (PrPSc). Like human peripheral blood, the peripheral blood of scrapie-infected sheep remains one possible source of disease transmission. As a first step in understanding the disease requirements in the natural scrapie host, the presence of PrPc was evaluated in peripheral blood cells from five normal and five scrapie-infected Suffolk sheep.
Design and methods: Live peripheral blood cells from normal and scrapie-infected sheep were analyzed for the presence of PrP using flow cytometry and reverse transcriptase-polymerase chain reaction (RT-PCR).
Results: PrP mRNA was detected in peripheral blood mononuclear cells (PBMC) but not in platelets or granulocytes. Consistent with PrP mRNA expression, cell-surface expressed PrP was detected on PBMC, but was not detected on granulocytes, platelets, or erythrocytes. Two-color flow cytometric analysis of PBMC specific phenotypes revealed that regardless of scrapie-status, expression of PrP was significantly higher on B2 positive B-lymphocytes than on CD4, CD8, WC1 positive T-lymphocytes or CD14 positive monocytes. In addition, PrP expressed on PBMC from normal and scrapie-infected sheep was sensitive to proteinase K (PK)and phosphatidylinositol-specific phospholipase C (PIPLC).
Interpretation and conclusions: Regardless of the scrapie-status of the sheep, resting PBMC transcribe PrPc and express PrPc as a cell-surface protein sensitive to both PK and PIPLC. Because of the abundance of PrPc on PBMC, future diagnostic tests using PK and PIPLC to discriminate between protease sensitive and resistant PrP must be carefully evaluated.