Comparing affinity of PrP-specific antibodies between 171Q and 171R variants of ovine PrP. (a) Western blot of 171R and 171Q recPrPs. The 171Q-dependent MAb SAF84 binds with the 171Q allele but not with the 171R variant, while reference MAb L42 binds equally well to both 171Q and 171R recombinant PrP variants. (b) PrPres material from a scrapie-positive VRQ/VRQ sheep (Q/Q lane) reacts equally strongly with both MAbs L42 and SAF84. Likewise, PrPres of scrapie-positive ARR/VRQ sheep (R/Q lane) remained equally strongly reactive with both L42 and SAF84, yielding nearly equal SAF84/L42 ratios that were statistically significantly equal by the two-sided Student t test (P = 0.18). For sample loading, 40 and 8 ng recombinant PrP was applied in the left and right lanes, respectively (a), and 0.5 mg TE was applied for the scrapie samples (b). Concentrations used for L42 and SAF84 antibodies were 0.1 and 0.5 μg/ml, respectively. Arrows indicate molecular mass markers (in kDa). The SAF84/L42 ratios below the blots are calculated from digitalized film images of blotting results for eight different 171R/Q cases and eight different 171Q/Q (2 ARQ/ARQ, 6 ARQ/VRQ) cases.