Classical scrapie prions in ovine blood are associated with B lymphocytes and platelet-rich plasma

Abstract

Background: Classical scrapie is a naturally occurring transmissible spongiform encephalopathy of sheep and goats characterized by cellular accumulation of abnormal isoforms of prion protein (PrPSc) in the central nervous system and the follicles of peripheral lymphoid tissues. Previous studies have shown that the whole blood and buffy coat blood fraction of scrapie infected sheep harbor prion infectivity. Although PrPSchas been detected in peripheral blood mononuclear cells (PBMCs), plasma, and more recently within a subpopulation of B lymphocytes, the infectivity status of these cells and plasma in sheep remains unknown. Therefore, the objective of this study was to determine whether circulating PBMCs, B lymphocytes and platelets from classical scrapie infected sheep harbor prion infectivity using a sheep bioassay.Results: Serial rectal mucosal biopsy and immunohistochemistry were used to detect preclinical infection in lambs transfused with whole blood or blood cell fractions from preclinical or clinical scrapie infected sheep. PrPScimmunolabeling was detected in antemortem rectal and postmortem lymphoid tissues from recipient lambs receiving PBMCs (15/15), CD72+B lymphocytes (3/3), CD21+B lymphocytes (3/3) or platelet-rich plasma (2/3) fractions. As expected, whole blood (11/13) and buffy coat (5/5) recipients showed positive PrPSclabeling in lymphoid follicles. However, at 549 days post-transfusion, PrPScwas not detected in rectal or other lymphoid tissues in three sheep receiving platelet-poor plasma fraction.Conclusions: Prion infectivity was detected in circulating PBMCs, CD72+pan B lymphocytes, the CD21+subpopulation of B lymphocytes and platelet-rich plasma of classical scrapie infected sheep using a sheep bioassay. Combining platelets with B lymphocytes might enhance PrPScdetection levels in blood samples. © 2011 Dassanayake et al; licensee BioMed Central Ltd.