Dec. 4, 2006 -- A protein abundant in multiple sclerosis patients during disease flare-ups may be a key culprit in this and other autoimmune diseases.

The protein is called osteopontin. Several years ago, Stanford researcher Lawrence Steinman, MD, and colleagues found abnormally high osteopontin levels in parts of the brain affected by MS flare-ups.

Now Steinman and colleagues find that in three different mouse models of MS, osteopontin causes disease relapse and makes disease symptoms worse.

The reason: osteopontin protects immune cells that have gone haywire and attack the brain. Normal protective mechanisms trigger self-destruction in aberrant immune cells. But osteopontin stops this signal, prolonging the lives of these cells.

Steinman's team is working on antibodies to block osteopontin. But Steinman admits there may be a problem with this approach. Osteopontin seems to play a major role in many normal body functions.

"Like a lot of important biological molecules, osteopontin has a Janus-like quality -- a bad side and a good side," Steinman says in a news release. "We're going to be extremely lucky if we give the antibody opposing osteopontin and derive just the good side."

The new findings appear in the Dec. 3 advance online edition of Nature Immunology.

SOURCES: Hur, E. Nature Immunology, advance online edition, Dec. 3, 2006. News release, Stanford University.