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Ultrasensitive method for the diagnosis of prion diseases

Max Planck Society : 09 May, 2000  (Technical Article)
German scientists have developed a novel, highly sensitive technique for the detection of prions, the infectious agents of Creutzfeldt-Jakob disease and BSE. By this method, single prion particles can be identified in body fluids. For the first time, prions could be detected in the cerebrospinal fluid of CJD patients. Currently, a clinical test to be used on a routine basis is being developed. (J. Bieschke, A. Giese, W. Schulz-Schaeffer, I. Zerr, S. Poser, M. Eigen, H. Kretzschmar: 'Ultra-sensitive detection of pathological prion protein aggregates by dual-color scanning for intensely fluorescent targets' Proc. Natl. Acad. Sci. USA (2000) 97:5468-5473).
Creutzfeldt-Jakob disease in humans and BSE in cattle belong to a group of transmissible and invariably fatal diseases of the central nervous system. They are caused by unusual infectious agents known as prions. Prions lack a detectable genome. They consist of a pathological aggregated form of a host-derived protein called prion protein. The definite diagnosis of prion disease is based on the demonstration of pathological prion protein accumulation in brain tissue, however, suitable clinical tests for the detection of prions in living patients or animals have not been available.

A novel diagnostic technique now exists that permits direct detection of prions in the cerebrospinal fluid, which is easily accessible for diagnostic purposes. Supported by the German Federal Ministry of Research, this method was developed in a cooperative effort by two research groups, that of the Nobel laureate, Manfred Eigen of the Max-Planck Institute of Biophysical Chemistry in Göttingen, and that of the prion researcher, Prof. Hans Kretzschmar of the University of Göttingen (now at the University of Munich).

This technique is based on a setup designed for confocal, dual-color fluorescence cross-correlation spectroscopy. Following excitation with a highly focussed laser beam, this setup permits the detection of single, fluorescently labeled molecules. By using specific antibody probes, the Göttingen scientists were able to label prion particles in cerebrospinal fluid with fluorescent dyes. The single prion particles could then be identifed with high sensitivity by scanning the sample with a laser beam (scanning for intensely fluorescent targets, SIFT). The sensitivity of this method is clearly superior to established detection techniques such as 'Western Blot' analysis.

By using the new technique in a pilot study at the University Hospital in Göttingen, prion particles were detected for the first time in the CSF of several CJD patients in a German CJD study supported by the German Federal Ministry of Health, but not in the CSF of control patients. This agent-specific test may in future be the basis of a quick and sensitive clinical test for CJD and other prion diseases. Since the technique can also be used to detect other disease-associated protein particles, it could also be applied for the early diagnosis of related diseases such as Alzheimer’s.
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