Effect of Mouse Peritoneal Macrophages on Scrapie Infectivity during Extended in vitro Incubation

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Abstract
Mouse peritoneal macrophages were exposed to scrapie (ME7 strain) brain homogenate in vitro for 2 h at 37c. The samples were assayed for infectivity by analysis of scrapie incubation periods and their values compared to those obtained after extended (1–28 days) in vitro incubation. The scrapie incubation periods for scrapie agent-macrophage mixtures which had undergone extended in vitro incubation were longer than for mixtures assayed after a 2-hour exposure to the scrapie agent. The difference in scrapie incubation periods was more drΕmatic when residual scrapie was eliminated by washing the cells after the 2-hour exposure to brain homogenate. The scrapie incubation period also increased following in vitro incubation of ME7 in the absence of cells; however, the changes were less than those observed for scrapie agent-macrophage mixtures. In a culture in which cells had been destroyed by UV irradiation after exposure to the scrapie agent, there was more scrapie infectivity than in a comparable culture of untreated, scrapie-Εxposed macrophages. These results show that scrapie infectivity decreases with extended incubation of scrapie-exposed macrophages, and the data suggest that macrophages can inactivate the scrapie agent in vitro.

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