A new antibody capable of locking onto the prion proteins that cause brain-wasting mad cow disease - and similar human ailments - has been developed by researchers, allowing early diagnosis and maybe even a vaccine.

The deformed 'prion' proteins which cause the diseases carry a distinct genetic signature that antibodies - immune system proteins in the body - can be trained to recognise, the international team of scientists report in the latest issue of the journal Nature Medicine.

Led by Professor Neil Cashman of Canada's University of Toronto, the team is already working on a vaccine using the new antibody.

"If we did get a vaccine, it would be wonderful to use in cattle and sheep, and deer and elk, to prevent these diseases," Cashman said. "But for humans that are developing symptoms, probably a vaccine would not be the way to go. Probably passive infusion of prion-specific antibodies would be the way to go."

The conventional way of 'training' the immune system to recognise an invader is to grind the infectious agent up and inject this into the body, prompting the production of antibodies that target the invading agent. But this method has been tried on prions for 15 years without success.

"My group decided to examine it from the sub-molecular level - to determine if antibodies would recognise and react to the amino acids exposed at the surface of a prion," Cashman said. "It was a novel idea, and when we found that our hypothesis actually worked, we were surprised and pleased."

Bovine spongiform encephalopathy (BSE), or mad cow disease, is back in the headlines after a Canadian cow was found to be infected. Countries that import beef from Canada, including Australia, have suspended imports while the case is investigated.

BSE swept through British cattle in the 1980s, forcing the slaughter of millions of beasts. Some people who ate contaminated beef during that time have since developed a human form of the disease - variant Creutzfeldt-Jakob disease (vCJD). According to the World Health Organisation, 139 people have been diagnosed with vCJD; most have died.

Fatal diseases

Both BSE and vCJD are members of a family of diseases called transmissible spongiform encephalopathies (TSEs). They are always fatal, and there is no cure or treatment. They often take years to develop, destroying the brain by eating holes in it.

In 1990s, scientists discovered that normal prion proteins, which have been compromised and folded into rogue shapes, cause these diseases and can warp healthy proteins simply by touching them.

Sheep get a TSE called scrapie; deer and elk develop chronic wasting disease; and cats, mink, mice and other animals can be infected. Humans are susceptible to several TSEs, including vCJD, kuru (found in populations where cannibalism is practised), and the better-known Creutzfeldt-Jakob disease, which occurs for unknown reasons in about one in a million people.

TSEs can only be definitively diagnosed after death, by looking at the damaged brain. "For blood screening, and for the screening of herds, one would want to have a non-invasive test," Cashman said. His team's antibody may provide this - providing a boon to blood banks and cattle farmers around the world.

Mad cow experts in Britain have developed a tonsil test for vCJD. But it requires a sample to be taken from a person's throat and, if the test is positive, there is no treatment that can be offered.

Cashman said it is unclear if infusing antibodies into a vCJD patient would help. The approach works short-term in other diseases, such as severe acute respiratory syndrome (SARS) and hepatitis.

"There is no science yet for how long it [the infective prion] takes to go away," he said. "These things we'd really have to find out from scratch."

Cashman's team, which included researchers in Britain and the United States, worked with two U.S. companies: IDEXX Laboratories Inc, which develops veterinary treatments, and privately-held Caprion Pharmaceuticals Inc.

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