A separate study using sPMCA 40 demonstrated that Mabs 3F4 and 5D6 caused complete inhibition of PrP Sc formation at 12-50 mg/ml (Fig. 4) . Therefore we extended those studies and evaluated the effects of Mabs 3F4 and 5D6 using a wider range of Mab concentrations (1.5-50 mg/ml). Compared to the other antibodies in this study, Mabs 3F4 and 5D6 had the most pronounced effects on PrP Sc formation as demonstrated by the low concentrations of 3 and 6 mg/ml, respectively, causing complete inhibition (Fig. 4) . The potent inhibitory effect of 5D6 on PrP Sc observed using sPMCA 40 coincides with its dramatic effect in the N2a/22L culture model. Furthermore, the poor PrP Sc inhibition by 3A2 with sPMCA 40 (Fig. 3B) corresponded well with the poor inhibition (only 32% reduction compared to negative control) observed in the cell culture system ( Fig. 2A  and 2B ). 