October 3 (HealthDay News) -- A protein that helps keep immune cells quiet -- and has been suspected of being tied to multiple sclerosis -- is more abundant in the spinal fluid of people with MS than those without the disease, a new report says.

The finding, by researchers at Washington University School of Medicine in St. Louis, may help give scientists new drug therapies to prevent and treat MS, which is caused by misdirected immune attacks on the protective lining that coats nerve cell branches.

The extra protein, TREM-2, was found floating freely in spinal fluid. It previously had only been seen on the surface of immune cells.

"This is only speculation for now, but these 'free agent' copies of TREM-2 could be making it harder for the TREM-2 that is attached to immune cells to keep the cells' aggressiveness under control," study lead author Dr. Laura Piccio, a postdoctorate fellow, said in a university news release.

TREM-2 is a receptor protein, although scientists don't yet know what molecule attaches to it and activates it. The research team suspects the TREM-2 in the spinal fluid could be binding to that unknown molecule, slashing the chances that it has to bind to and activate TREM-2 attached to immune cells.

The findings were published in the journal Brain.

It is estimated that 400,000 people in the United States have MS, a disease that often strikes in episodic bursts, causing bladder and bowel dysfunction, memory problems, fatigue, dizziness, depression, difficulty walking, numbness, pain and vision problems.

Previous research has shown that when activated, TREM-2 can help reduce immune inflammation and promote phagocytosis, a process that lets cells consume things. Researchers think this allows macrophage, an immune cell that performs a variety of housekeeping functions, to consume dying nerve cells and shut down inflammatory processes.

"The main thing we knew about MS and the function of TREM-2 before this study was that blocking TREM-2 in a mouse model of MS made their conditions worse," study senior author Dr. Anne Cross, head of the school's neuroimmunology section, said in the news release.

SOURCE: Washington University School of Medicine, news release, Sept. 29, 2008