Protein Misfolding Cyclic Amplification (PMCA), a PCR-like technology to amplify misfolded, disease-associated prion proteins gains widespread acceptance in the prion research community. Improvements in PMCA technology and its application for human vCJD prions were presented at Prion 2007 held in Edinburgh in September 2007. The findings pave the way to more sensitive blood-based screening tests for human blood banks.
Prion diseases can be transmitted via blood transfusions. The presence of infectivity in blood of vCJD patients demands special measures to prevent the spread of the disease via transfusions. That makes the development of sensitive and specific ante mortem tests for donor screening one of the major focal points in research today. The difficulty in finding prions (PrPSc) their very low concentration, which is presumed to be 1000 x lower than that found in the brain. Recent developments in the amplification of prions in blood might help solve this problem.
Improved prion amplification
Increased sensitivity might be achieved by the amplification of PrPSc in blood samples. The protein misfolding cyclic amplification (PMCA) uses PrPSc present in a positive sample as a seed. Normal PrP in the sample is converted to PrPSc (see figure). Using this method, Castilla and coworkers have succeeded last year in detecting PrPSc in the blood of hamsters that were experimentally infected with TSE. The reproducibility of the PMCA method developed thus far was hampered by the fact that the method used brain homogenate as a source of normal PrP (PrPC), a material that contains numerous other biological substances and can therefore not be standardized. Byron Caughey and coworkers have now overcome this problem and succeeded in the replication of prions using recombinantly produced PrP. Furthermore, this group has replaced the sonication step, included to disperse the aggregates, with a shaking step to further enhance the reproducibility of the method. With these adaptations the PMCA amplification method seems a promising tool for increasing the sensitivity of a TSE blood test.
