Replication of the Factor in Scrapie Material That Causes a Decrease in Polymorphonuclear Neutrophils

Previous work has shown that homogenates of brain from mice infected with scrapie contain a factor that reduces the percentage of polymorphonuclear neu-trophils (PMNs). In the present work, the titer of this factor was found to be approximately 106 times greater than the infectivity titer for scrapie. The PMN factor replicated l Ov-fold in mice that never showed signs of scrapie disease, i.e., mice inoculated with approximately 6 X 10-4 LD50 units of scrapie. Inoculation of mice with 1012 units of the PMN factor, which had been produced in the absence of scrapie infectious units, failed to cause scrapie disease. Scrapie is a slow, progressive infectious disease of sheep and goats that has been transmitted to mice [1-3]. The incubation period for clinical disease in mice is approximately four months after intracerebral inoculation. In previous work [4], we observed a decrease in the percentage of polymorphonuclear neutrophils (PMNs) in th