Aug. 17, 2007 -- Mice with an MS-like disease got sicker faster after being chased and bitten by aggressive mouse bullies.
MS -- multiple sclerosis -- is an autoimmune disease in which the immune system attacks the myelin sheath protecting nerve cells. Nobody knows exactly what triggers recurrent relapses and new brain lesions in people with MS. There's some evidence that stress plays a role.
To investigate this issue, psychologist Mary W. Meagher, PhD, and colleagues at Texas A&M University infected young male mice with a virus that eventually triggers MS-like autoimmune responses. Three of these mice were housed in a cage. Over several weeks, they established a stable social hierarchy.
Meanwhile, the researchers selected a number of older, more aggressive mice. These bully mice were chosen because they were quick to attack other mice.
Two hours a night, three nights in a row, one of these mouse bullies was put in the cage with the younger, virus-infected mice. After a night off, the infected mice underwent another three nights of harassment by the bully mice. To prevent social bonding, a different bully mouse was used for each session.
The mouse "intruders," Meagher and colleagues note, engaged in "observable aggressive behaviors" -- "posturing, fighting, wounding, and pursuit."
Sure enough, the stress got to the virus-infected mice. Their immune systems were less able to fight off illness than mice that had not been bullied. And their MS got worse, faster, than the MS of less stressed mice.
"Similar to mice exposed to repeated social defeat by an aggressive intruder, people exposed to chronic social conflict experience high levels of stress and consequent dysregulation of the immune system, thereby increasing vulnerability to infectious and autoimmune disease," Meagher says in a news release.
Meagher and colleagues presented their findings at the annual meeting of the American Psychological Association, held Aug. 17-20 in San Francisco.