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The Marker Abnormal form of PrP (PrP tse , PrP res , PrP*) (not well defined; a correlate of infection)

Objective To define a process such that if an assay method successfully completes it, it is justifiable to try it in the Blood Transfusion Service at some scale. The Marker Abnormal form of PrP (PrP tse , PrP res , PrP*) (not well defined; a correlate of infection).

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The Marker Abnormal form of PrP (PrP tse , PrP res , PrP*) (not well defined; a correlate of infection)

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  1. ObjectiveTo define a process such that if an assay method successfully completes it, it is justifiable to try it in the Blood Transfusion Service at some scale.

  2. The MarkerAbnormal form of PrP (PrP tse, PrP res, PrP*)(not well defined; a correlate of infection)

  3. The analyteBloodPlasmaSerumLeucocytes(infectivity low, form of PrP tse undefined)

  4. The internal run controlNon-infectious (recombinant or non human)Tissue of high titreBlood(assays must work on different species, maybe different tissues)

  5. Question 1How good is the assay at detecting the marker?(sensitivity, specificity)

  6. Question 2How good is the marker at predicting the presence of infectivity in blood?(suitability)

  7. Question 3How good is the marker at predicting eventual disease?(clinical significance, ethics of donor notification)

  8. Process (1)Assay on human brain and spleenAssay on brain and spleen diluted in plasmaAssay blinded and replicate blood samples from scrapie positive and negative animals. Shows that the assay measures something in tissues known to be infectious; establishes sensitivity compared to other methods (like immunoblot). Shows that it will or will not record a signal consistently in a sample which may be positive and not in similar samples expected to be negative

  9. ProcedureAll producers test aliquots of the same samples. This is for cross confirmation.The procedure will only work if the assays work equally well on a variety of speciesTesting on samples from known vCJD positive or at risk cases will be minimal. Validity of the tests will be based on animal samples.

  10. Samples tested by all candidate assays 1. Samples from sheep from scrapie endemic flock: some should be detected consistently positive on repeat testing. 3. Samples from sheep from a scrapie free flock. All should be consistent and possibly consistently negative. 4. Samples from UK blood donors. Should be consistent. Could detect three real positives per 10000 samples.5. Samples from other blood donors should be consistent; should detect fewer positives than the UK samples6.Samples from vCJD patients: some should be consistently positive

  11. Samples tested by all candidate assays 1.‘Seroconversion panels’ from mice or sheep: some should be positive sometime before disease.2. Samples from vCJD exposed transfusion recipients: some should be positive before disease, if there is any disease.3. Samples from Haemophiliacs: some should be positive before disease, but there is not likely to be much disease (none so far).

  12. If a test detects brain and spleen to high sensitivity, scores appropriate animal and human blood samples consistently positive, scores ‘seroconverting’ samples consistently positive, scores three of 10000 UK donations positive and none of 10000 US donations positive, and gives the same results for all samples as another test working on a different principle, and if it is easy to implement:Can you turn it loose on the Blood Transfusion Service?If so, how?If not what do you do next?

  13. Materials currently aliquoted, archived and available for use from NIBSC. Sporadic CJD (1): grey matter enriched cerebral cortex, MM homozygous Sporadic CJD (2): grey matter enriched cerebral cortex, MM homozygous vCJD (1): grey matter enriched cerebral cortex, MM homozygous Control Brain: grey matter enriched cerebral cortex, MM homozygous vCJD (2): grey matter enriched cerebral cortex, MM homozygous Sporadic CJD: grey matter enriched cerebral cortex, MV heterozygous vCJD spleen (1): MM homozygous vCJD spleen (2): MM homozygous normal spleen: MM homozygous Scrapie infected brain (1): frontal cortex, cerebellum,thalamus,midbrain,medulla. Scrapie infected brain (2): frontal cortex, cerebellum,thalamus,midbrain,medulla Scrapie infected spleen (1) Scrapie infected spleen (2) Scrapie infected blood (1): whole blood, buffy coat, erythrocytes, plasma Scrapie infected blood (2): whole blood, buffy coat, erythrocytes, plasma Non infected bovine BSE suspect (1) brain, spleen, blood Dilution series of vCJD brain and spleen in plasma. Tissues were homogenised at 10% w/v in .25M sucrose where required. Several hundred aliquots of each preparation are available.

  14. Materials soon to be available1. Blood donor specimens from UK2. Sequential sera from UK haemophiliacs from 1970s on3. Sequential sera from infected sheep.4. Sequential sera from infected miceCJD Resource Centrewww.nibsc.ac.uk/cjd

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