Infection route-independent accumulation of splenic abnormal prion protein

The accumulation kinetics of the abnormal form of prion protein (PrP(Sc)) in spleens and brains of scrapie (Obihiro-1)-infected mice at various times after intracerebral (i.c.), intraperitoneal (i.p.), or oral inoculation were studied. PrP(Sc) was first detected by Western blotting with anti-prion protein antibodies on days 70 and 116 after i.c. (3 microg) in spleens and brains, respectively. Although the amount of cerebral PrP(Sc) gradually increased to the maximum level on day 152 after i.c. inoculation, splenic PrP(Sc) established the maximum level on day 116 after i.c. inoculation then registered slight decreases up to day 152 with further incubation. The detectable levels of cerebral PrP(Sc) by Western blotting were established on day 231 or 259, whereas those of splenic PrP(Sc) were detected on day 94 or 93, after i.p. and oral infection, respectively. The splenic PrP(Sc) decreased slightly thereafter. These results indicate that splenic PrP(Sc) increased before cerebral PrP(Sc) established a detectable level in a manner independent of the inoculation route.