Different levels of prion protein (PrPc) expression on hamster, mouse and human blood cells

The host prion protein, PrPc, and its conformationally changed isoform, PrPsc, play an essential role in the transmissible spongiform encephalopathy (TSE) infections. The prion hypothesis postulates that PrPsc is the TSE infectious agent and that it serves as a template to convert host PrPc to additional PrPsc. Blood of experimentally TSE-infected rodents has been shown to contain TSE infectivity. If blood-borne TSE infectivity requires association with PrPc, differences in the distribution of PrPc in blood could affect the amount and distribution of blood-borne infectivity in different hosts. We have compared the distribution of PrPc on the peripheral blood cells of humans, hamsters and mice using quantitative flow cytometry. Human lymphocytes, monocytes and platelets displayed much greater quantities of PrPc than corresponding mouse cells. Mouse platelets did not express any detectable PrPc. A similar low level of PrPc was found on both human and mouse red blood cells. None of the hamster peripheral blood cells displayed detectable amounts of PrPc. If PrPc contributes to the propagation or transport of TSE infectivity in blood, the species differences in PrPc distribution reported here need to be considered when extrapolating the results of rodent TSE transmission studies with blood and blood components to humans.