To establish PrPSc-specific mAbs, we immunized Pmp(-/-) mice with PrPSc purified from prion-infected mice. Using this approach, we obtained mAb 6H10, which reacted with PrPSc treated with proteinase K, but not with PrPSc pretreated with more than 3 M GdnHCl. In contrast, reactivity of pan-PrP mAbs increased with increasing concentrations of GdnHCl used for pretreatment of PrPSc. In histoblot analysis, mAb 6H10 showed a positive reaction on a non-denatured histoblot but reactivity was lower when the histoblot was pretreated by autoclaving. Epitope analysis suggested that the extreme C-terminus of PrP is likely to be part of the epitope for mAb 6H10. MAb 6H10 immunoprecipitated PrPSc from brains of mice, sheep, and cattle infected with prions. Furthermore, pretreatment of purified PrPSc with mAb 6H10 reduced the infectious titer more than 1 log. Taken together, these results suggest that mAb 6H10 recognizes a conformational epitope on PrPSc that is related to prion infectivity. (C) 2009 Elsevier Inc. All rights reserved.