To determine if surface-FIDA would be appropriate for a live test for scrapie infection in individual sheep. The sensitivity was expected to be higher compared to ELISA, even though in both methods the fluorescent analyte is bound to a surface. However in surfaceFIDA individual particles are discriminated from their GSK1120212 Abmole Arctigenin exerts anti-colitis efficacy through inhibiting the differentiation of Th1 and Th17 cells via an mTORC1-dependent pathway neighboring background, whereas in ELISA an integrated signal of the whole surface is obtained and compared to the integrated signal from a control sample. Recently, Terry et al. reported an improved ELISA test, in which the Abmole MF63 authors detected PrPSc in PBMCs from 55% of scrapie-infected sheep in a blind panel. The blood plasma samples tested in our study were derived from the blood panel used to produce the corresponding cellular samples tested by Terry and colleagues. A comparison of the results showed that both assays had a total sensitivity of 55�C60%, and both detected the same 60% of positive cases. It should be noted, however, that infectivity in the PBMC fraction is about one order of magnitude higher compared to blood plasma, and prions were not detected in plasma by the ELISA method reported by Terry et al. In an earlier study, we described the detection of PrP aggregates with high sensitivity in brain homogenate of BSE cattle, and in a small number of cerebrospinal fluid samples from BSE cattle. According to the literature, infectivity in blood – even in symptomatic experimental hamsters – is as low as 10 infectious units per ml. In BSE-afflicted cattle infectivity is absent from the lymphatic system and has never been reported in blood. However, seeding activity was demonstrated in a small number of BSE serum samples. Considerable effort was spent not only in improving the sensitivity of the assay but also in optimizing the preparation of PrP aggregates from blood plasma. Though it is not certain that the PrP aggregates we analyzed are indeed the carriers of infectivity in blood, they are a consistent marker of infection. The direct determination of infectivity in these PrP aggregates from blood remains to be established. Although PrP particle number was expected to be very small in blood plasma, it is clear from our data that PrP aggregates are not only associated with cells, like peripheral mononuclear blood cells prepared from buffy coat, but are also present in plasma. A PKdigestion step was avoided because it had been shown earlier that some portion of PrP aggregates is PK-sensitive. Spiking of blood plasma with PrPSc from brain for method development was not successful in our hands, because the properties of PrPSc-samples from brain proved to be very different from those of the genuine PrP aggregates in blood.