The latest salvo in the prion debate.

"Researchers Rule Out Proteins As Cause of 'Mad Cow' Disease" blazed the headline in the Jan. 17 Washington Post. Don't believe everything you read, however. When it comes to mad cow disease, all results remain open to interpretation.

The Post story, and similar articles elsewhere, centered on an unexpected experimental result described in the Jan. 17 Science. A research group headed by Dominique Dormont of the Atomic Energy Commission in Fontenay-aux-Roses, France, ground up brains of cows with bovine spongiform encephalopathy (BSE), the fatal neurodegenerative disorder also known as mad cow disease. The scientists then injected samples of the bovine brains into the brains of 30 mice.

After periods ranging from 368 to 719 days, all of the mice began experiencing symptoms of a BSE-like neurological disorder. Yet when the scientists searched the brains of those mice for prions, they found none in 55 percent of them. That was surprising, since prions are now thought by many scientists to be the infectious agent for BSE. According to this hypothesis, prions are malformed versions of a cellular protein called PrP. Prions cause BSE by converting normal PrP proteins into their own, misshapen form.

Once ridiculed, the prion hypothesis has slowly gained a following among scientists (SN: 9/24/94, p. 202). Because they did not detect these abnormal proteins in the brains of all the diseased mice, however, Dormont and his group speculate that prions are not the agent for BSE. Still, the prions probably play a crucial role in how the disease develops, they note.

While the few researchers who argue that an undetected virus or bacterium causes BSE have taken heart from the results of the French group, other scientists are skeptical. "Our experience is quite different than the French group's," observes Moira E. Bruce of the Institute for Animal Health in Edinburgh, whose research group has also injected BSE brain tissue into mice. The most important distinction, Bruce notes, is that in every mouse tested so far, her group has found accumulations of prions.

Bruce argues that the work of Dormont's group does not shatter the prion hypothesis, but she also remains undecided as to whether prions or some infectious microbe causes BSE. Like many other scientists, "I'm still on the fence," she says.