THE century-old assumption that multiple sclerosis is an autoimmune disease is under attack. Treatments based on the autoimmune theory have failed so miserably, say a group of doctors, that it is time to look for other explanations.
In a lengthy review to be published next week in The Journal of the Royal College of Physicians of Edinburgh, the three neurologists dispute the received wisdom that the disease wreaks its havoc when immune cells attack and destroy myelin protein, which insulates nerves and helps them conduct signals. Instead, they back an emerging theory that MS is caused when support cells called astrocytes malfunction, perhaps as a result of genetic and environmental triggers.
Many mainstream MS researchers contacted by New 杏吧原创 have poured scorn on the review. But a few agree it鈥檚 time for a rethink.
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Peter Behan and Abhijit Chaudhuri at the University of Glasgow and Bart Roep of the Leiden University Medical Centre pull no punches in their attempts to demolish the prevailing theory. They begin by attacking the animal experiments that have underpinned the autoimmune theory since the late 19th century.
Back then, researchers discovered that if they injected nerve or brain tissue into an animal, its immune system would attack the nervous system. They called this experimental allergic encephalomyelitis, and before long adopted EAE as the 鈥渁nimal model鈥� of multiple sclerosis.
This, say the heretics, was a big mistake. In their view, EAE is completely different from MS. 鈥淭here are huge differences, and they鈥檝e been skipped over,鈥� Behan told New 杏吧原创.
For instance, EAE either kills animals or leaves them with permanent disabilities. 鈥淚t doesn鈥檛 come and go like MS,鈥� he says. Animals with EAE also suffer severe nerve inflammation, whereas in MS inflammation is usually mild, if present at all.
Despite this, virtually all treatments for MS have been tested on EAE. Little wonder then, says Behan, that the treatments do not work for people. 鈥淣ot a single human has been cured using these approaches,鈥� he says.
However, steroids and other immunosuppressants do work for a brain disease called acute disseminated encephalomyelitis, a rare result of infections. Behan thinks ADEM, not MS, is the human equivalent of EAE.
He also argues that the fact that traces of white blood cells are found at some sites of nerve and brain damage in MS patients does not prove they caused the damage. The same traces are found after strokes and neurodegenerative diseases.
Instead, the group backs the idea that malfunctioning astrocytes, cells that support and nourish neurons, might be to blame for MS. Behan says there is increasing evidence that astrocytes go awry in MS sufferers. 鈥淭hey go crazy, and multiply like mad,鈥� he says.
The damage then starts to spread, perhaps triggered by an as-yet unidentified chemical messenger. Behan speculates that releases of this factor correspond to periods of deterioration in MS patients.
Finally, the group says that MS and other diseases involving astrocytes have all been linked to regions of chromosome 17. These diseases include gliomas 鈥� essentially cancers of astrocytes 鈥� and the abnormal growth of either astrocytes or myelin-producing Schwann cells, which is known as neurofibromatosis. The resulting overgrown nerves are sometimes found in patients with MS.
鈥淭hese diseases are all under the influence of genes on chromosome 17,鈥� Behan says. An environmental trigger might set off the disease in people with mutations in these genes.
Mainstream researchers reject many of these arguments. 鈥淚t鈥檚 presented as a comprehensive review but is highly selective,鈥� says Stephen Reingold, vice-president of research at the National Multiple Sclerosis Society in New York.
He accepts that EAE is not a perfect model for MS, but claims it has been used successfully to model aspects of demyelination. Charles Poser of Harvard Medical School agrees. Behan鈥檚 paper fails to acknowledge the exact match between the damage in people with MS and that in marmoset monkeys with EAE, he says.
The traditionalists also dispute Behan鈥檚 claims that no treatments have worked and that the latest drugs for MS 鈥� notably glatiramir acetate and beta interferons 鈥� are little better than placebos. 鈥淣one are cures,鈥� admits Reingold. 鈥淏ut the immunoregulatory agents do provide relative benefits鈥nd there are dozens of publications and regulatory approvals worldwide that attest to this.鈥�
As for the astrocyte theory, Reingold says whatever the cause, the early phases of MS may be 鈥渕ore inflammatory in nature鈥�, and therefore should be treatable with immunotherapy.
And the idea that a common genetic fault links MS to astrocyte diseases is rejected by Alastair Compston of Cambridge University, who first suggested a link between MS and a region of chromosome 17 six years ago and is now trying to identify specific genes. He says that the region linked with MS is different from the one, also on chromosome 17, linked to neurofibromatosis. And he knows of no link to glioma on chromosome 17.
But not everyone is as dismissive. 鈥淚 don鈥檛 think anyone has convincing evidence that immunosuppression is helpful in the long run,鈥� says neurologist George Ebers of Oxford University. And it is unclear if the white blood cells found around damaged areas are there to attack or to repair them, he admits. But while the evidence that MS is autoimmune is circumstantial, he adds, it is reasonably strong.
Israel Steiner, a neurologist at the Hadassah University Hospital in Jerusalem, agrees that EAE has blocked 鈥渆ffective progress鈥� for decades. He thinks alternative theories should be put to the test. 鈥淚 definitely believe it鈥檚 high time to reconsider the entire field. It has not led us into understanding the disease or to a better therapy for patients,鈥� he says. 鈥淢any people in the community who do not have a vested interest in the autoimmune hypothesis share my views, but I鈥檓 not sure they would like to step out.鈥�
