Mitogenic stimulation of the host enhances susceptibility to scrapie

Abstract

THERE are several reasons for concluding that scrapie agents depend, for extraneural replication, on some components of the host's lymphoreticular system being functional¹. Agent replication occurs earliest in the spleen and lymph nodes² and some factors which make an animal more susceptible to infection by conventional viruses have the opposite effect with scrapie. For example, infection with scrapie by the intraperitoneal (i.p.) route is more difficult in neonatal than in adult mice³, in mice treated with a large dose of cortical steroids⁴ and in mice with severe malnutrition (A.G.D., unpublished). These findings raise the question whether the opposite effect can be produced, so that mice given treatments which stimulate any sector of the immune system would be infected more readily with scrapie agent given extraneurally. The results presented here confirm this expectation in mice treated with the mitogen phytohaemagglutinin (PHA), which increases the activity of lymphoreticular cells.