Multiple sclerosis (MS) has long been thought of as an autoimmune disease. But new research suggests that it's not immune cells that strip the insulation off neurons and cause neurological symptoms. Rather, the insulation may be disrupted when the cells that build it self-destruct.
In MS, the insulating layer of myelin around neurons degrades, leading to loss of muscle control, numbness, or cognitive problems. Most researchers have thought this happens when the victim's own immune cells move in on the myelin and chew it up, leaving plaquelike scars behind.
Now, neurologists Michael Barnett and John Prineas of the University of Sydney, Australia, have found evidence to the contrary. They autopsied 12 patients who died from MS shortly after suffering a bout of neurological symptoms. All of the patients had the plaquelike scars typical of MS. But contrary to all expectations, seven of them had intact myelin and little inflammation, the researchers reported online this week in Annals of Neurology. Equally surprising was that within the plaques, up to 30% of the cells that make the myelin coating appeared to be suicidal. The researchers conclude that MS isn't triggered by an autoimmune affront, but rather by something--possibly a virus--that instigates cell suicide. In this scenario the dead cells cause the immune response, not the other way around.
"The MS field is so focused on autoimmunity as its cause that we rarely hear an alternative hypothesis," says cell biologist Bruce Trapp of the Cleveland Clinic Foundation in Ohio. The study is refreshing, he says, because "the pathology of MS can't be explained by what we currently know." Experimental neuropathologist Moses Rodriguez of the Mayo Clinic in Rochester, New York, agrees that viruses are likely suspects. He says that the result could explain why some antiinflammatory treatments haven't helped and why an antiviral drug, interferon, is one of the best treatments.