No evidence for involvement of plasma proteins or blood-borne cells in amyloid plaque formation in scrapie-affected mice. An immunohistoperoxidase study.

The present study was designed to investigate blood-brain permeability and the possible involvement of plasma proteins and blood-borne cells in amyloid plaque formation in scrapie-affected mice. No abnormal extravasation of intravenously injected horseradish peroxidase (HRP) was found and with immunocytochemical techniques no plasma proteins were detected in neuropil from scrapie-affected mice. In contrast to an earlier report, these findings suggest that the blood-brain barrier is essentially intact in scrapie-affected mice. Using immunohistochemical and enzyme histochemical methods no cells belonging to the monocyte-macrophage lineage were detected in association with amyloid plaques. Thus, by these methods there was no evidence that plasma proteins or blood-borne cells are involved in amyloid plaque formation in scrapie-affected mice. However, astrocytes were consistently found to be associated with amyloid plaques at all stages of their development.