Differential constitutive and activation-dependent expression of prion protein in human peripheral blood leucocytes

The cellular isoform of the prion protein (PrPC) is a cell surface glycoprotein that has recently been shown to play a role in haemopoietic cell activation and proliferation. We have characterized the constitutive expression of PrPC on human peripheral blood (pB) cell populations, using PrP-specific antibodies in a multiparameter flow cytometry approach. We found that T cells, NK cells and monocytes exhibit similar PrPC levels, whereas PrPC surface staining on B cells was significantly lower and was virtually absent on granulocytes. Within the T-cell compartment, CD8+ cells showed a significantly higher PrPC expression than CD4+ cells. Similarly, CD3+ cells co-expressing the activation marker CD56 (N-CAM) exhibited significantly higher PrPC expression levels than their CD56- counterparts. Culture of CD14+ pB monocytes for 12-48 h in the presence of interferon gamma (IFN-gamma) resulted in a significant increase in PrPC expression in a time- and concentration-dependent manner. This effect was partially abrogated by the addition of the metabolic inhibitor cycloheximide, indicating the role of protein synthesis in this process. Our results show that PrPC expression on human haemopoietic cells correlates with the activation and developmental status of these cells, suggesting an important functional role of PrPC in the haemopoietic system.