Perivascular infiltrates of leukocytes in brains of scrapie-infected mice

Four chronic subacute spongiform encephalopathies-Kuru and Creutzfeld-Jakob diseases of man, transmissible encephalopathy in mink and scrapie in sheep-are caused by slow viruses with unconventional biological and biochemical properties(1-4). Since the transmission of the scrapie agent to mice(5) and the comparative histological analysis of Kuru in man(6) and of scrapie in the mouse, scrapie-mouse systems have become important models of spongiform encephalopathies. The predominant histopathological lesions (for review see refs 2, 4) found in these diseases result from nerve cell degeneration(7). It seems that, in contrast to diseases of the nervous system caused by conventional viruses, perivascular leukocyte infiltrations do not play any part in the progression of spongiform encephalopathies and it is not known whether leukocyte infiltrations can be induced by unconventional slow viruses. Here we report that scrapie infection can indeed produce such lesions in mice.