Scrapie strain-specific interactions with endogenous murine leukaemia virus.

The finding that a senescence-accelerated mouse (SAMP8) shows early brain ageing, with histopathological changes resembling those seen in scrapie, combined with the discovery of high levels of endogenous murine leukaemia virus (MuLV) in brains of SAMP8 mice prompted us to examine the effect of scrapie infection on MuLV titres in this strain and in one of its progenitors, the AKR strain. Three scrapie strains (ME7, 22L and 139A) that had a comparatively short incubation period in SAMP8 and AKR mice caused an increase in brain MuLV titres that was scrapie strain-specific: in each mouse strain, the greatest effect was with 1 39A, and the least with ME7. The 22A scrapie strain, which has a long incubation period in SAMP8 mice, did not affect MuLV titres in brains of this mouse strain. Previous analyses of scrapie incubation periods in AKR, SAMP8 and another strain derived from an AKR cross (SAMR1) showed an inverse relationship between brain MuLV titres and scrapie incubation periods. This finding, combined with the effect of scrapie on MuLV titres, suggests an interaction between the scrapie infectious process and MuLV replication.