Relative specific infectivity of various prion species.

ns, not significant. All determinations were in quadruplicate.*RI's were determined on PK1 cells (A) or LD9 cells (B) by the SSCA and expressed relative to the values found for C57[RML] (A) or C57[ME7] (B).+PrPres was determined by Sandwich ELISA as shown in Figure 1C and expressed relative to the values found for C57[RML] (A) or C57[ME7] (B).#Relative specific infectivity is the ratio RI/PrPres relative to that of C57[RML] (A) or C57[ME7] (B).The specific infectivity of GPI−[RML] is 6 times lower than that of C57[RML] prions, and that of GPI−/GPI−[ME7] is 25 times lower than that of C57[ME7] prions, underlining the changed properties of prions adapted to GPI− brain. After being returned to and propagated in wild-type brain, C57/C57/C57/GPI−[RML] prions (which show a novel, stable CPA response and constitute a novel strain, designated SFL) do not fully regain the specific infectivity of RML, however the difference is not statistically significant. ME7 prions fully regain the original specific infectivity on being returned from GPI− to wild-type mice.