Prion-related encephalopathies are characterized by the intracerebral accumulation of an abnormal isoform of the cellular prion protein (PrPC) named scrapie prion protein (PrPSc). The pathological forms of this protein and its cellular precursor are not only expressed in the brain but also, at lower concentrations, in peripheral tissues. We recently showed that a synthetic peptide corresponding to residues 106–126 [PrP-(106–126)] of the human PrP is toxic to neurons and trophic to astrocytes in vitro. Our experiments were aimed at verifying whether PrP-(106–126) and other peptides corresponding to fragments of the amyloid protein purified from brains of patients with Gerstmann–Sträussler–Scheinker disease – namely PrP-(89–106), PrP-(106–114), PrP-(127–147) – were capable of stimulating circulating leucocytes. Native PrP expression in human lymphocytes, monocytes and neutrophils was first confirmed using PCR amplification of total RNA, after reverse transcription, and immunoblot analysis of cell extracts with anti-PrP antibodies. PrP-(106–126), but not the other peptides, increased membrane microviscosity, intracellular Ca2+ concentration and cell migration in circulating leucocytes, and O2-•production in monocytes and neutrophils. Membrane microviscosity was determined by the fluorescence polarization technique, using diphenylhexatriene as a probe, 300 s after the addition of PrP-(106–126) to the cell suspension in the concentration range 5–50 µM. The increase in intracellular Ca2+ elicited by PrP-(106–126) was dose-dependent in the range 5–500 µM. PrP-(106–126) stimulated O2-•production in monocytes and neutrophils in a dose- (10–300 µM) and time-(5–30 min) dependent manner in the presence of 10 µM dihydrocytochalasin B. Both the increase in Ca2+ concentration and the O2-•production were partially sensitive to pertussis toxin. PrP-(106–126) stimulated leucocyte migration in a dose-dependent (30–300 µM) manner and, at the highest concentration used, this migration was comparable with that elicited by 2.5 nM interleukin 8 or 10 nM fMet-Leu-Phe peptide.

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In memory of Professor Alfredo Leonardi, General Secretary of the Mario Negri Institute from its foundation until April 1995.