A substance made by immune cells may play a key role in the development of multiple sclerosis, research suggests.
Some MS patients have problems with vision
A team at Ohio State University found the molecule blocked progression of a similar disease in mice.
The findings suggest blocking the molecule - macrophage migration inhibitory factor (MIF) - might be an effective way to treat MS.
The Journal of Immunology study also suggests testing for MIF may help predict flare-ups of illness.
The Ohio State team worked on mice bred to develop a disease which closely resembles MS.
They found animals with MIF developed the initial, acute phase of the disease, but then showed no signs of further progression.
Lead researcher Professor Caroline Whitacre said: "Our results suggest that MIF may be less important for initiating MS, but that it may be necessary for MS progression.
"These findings indicate that in the future we can perhaps use MIF levels to predict the onset of a relapse.
"But more importantly, perhaps this study will lead to drugs that can halt the course of MS by blocking the action of MIF."
MS is an autoimmune disease caused by the immune system turning in on itself and attacking the body's own tissues.
In MS, immune cells destroy the myelin sheath that surrounds nerve fibres in the brain and spinal cord and enables them to transmit impulses.
MS symptoms vary from person to person, but can include fatigue, numbness, tingling, loss of balance and difficulty walking.
In about 85% of cases, MS shows a pattern of remission and relapse with no warning as to when a relapse will occur.
The research suggests that MIF stimulates a chain of reactions that lead to the production of inflammation-producing chemicals.
Conversely, lack of MIF seems to trigger the release of other immune system chemicals that block inflammation.
Mike O'Donovan, chief executive of the MS Society, said: "The possibility that a way might be found to stop MS in its tracks is obviously encouraging and needs investigating further.
"Having said that, experience has taught us to be cautious because what works in the animal model does not necessarily work in humans."
Helen Yates, of the Multiple Sclerosis Resource Centre, said: "Whilst this study is only at the animal model stage, the identification of this potential gene factor in relation to MS is extremely interesting and offers great hope for the future."
Chris Jones, chief executive of the MS Trust, echoed concern that animal findings would not necessary translate to humans.