Prions, previously thought to accumulate mainly in the brain can also infect other organs

Prions, infectious proteins associated with bovine spongiform encephalopathy (BSE) or Mad Cow Disease, were previously thought to accumulate mainly in the brain, but Yale and University of Zurich researchers report in Science that other organs can also become infected.

Past research had shown that the brain and spinal cord bear the highest infection risk for BSE, followed by organs such as the spleen, lymph nodes and tonsils. All other organs were thought to be devoid of prions.

Ruddle and co-authors analyzed three organ systems that are typically free of prions: liver, pancreas and kidney, in five different mouse models of chronic inflammation. After the mice were infected with prions, the team detected prion accumulation in the inflamed organs. They concluded that the spectrum of organs containing prions might be considerably increased in situations of chronic inflammation.

"The study suggests that the current prion risk-classification of farm animal organs may need to be reassessed in animals suffering from inflammation due to microbial infection or autoimmune disease," said Nancy H. Ruddle, the John Rodman Paul Professor and Director of Graduate Studies in the Department of Epidemiology and Public Health at the Yale School of Medicine.

Previous research in Adriano Aguzzi's group at the Institute of Neuropathology at University of Zurich showed that B cells are essential for the spread of prions to organs other than the brain. B cells are found in lymphoid organs in healthy humans and animals, but they can migrate into non-lymphoid organs under inflammatory circumstances.

Other researchers on the study include first author Mathias Heikenwalder, Nicolas Zeller, Harald Seeger, Marco Prinz, Peter-Christian Klohn, Petra Schwarz, Charles Weissman and the director of the study, Adriano Aguzzi.

Ruddle's portion of this study was supported by National Institutes of Health Grant CA 16885.