Healthy Eve: Disorder's gender bias still unexplained
By Linda Carroll MSNBC
Sept. 17 - You do everything you can to keep your body healthy. You eat right. You exercise. You try to stay away from carcinogens. But what can you do if the enemy is within? What if your own body makes you sick? For the 350,000 Americans who suffer from multiple sclerosis - the vast majority of them women - this is the case.
THE DISEASE develops when the very same immune system that roots out and destroys invaders malfunctions and turns its weapons back on our nervous system.
Scientists aren't sure what makes the immune system turn on us and attack our myelin, the fatty material that insulates the nerves and allows them to transmit electrical signals almost instantaneously. Population studies have shown that certain families may inherit a susceptibility to developing the disorder.
VIRAL THEORY OF MS
Others think it may start with a virus. According to the theory, the immune system will target a person's myelin if the virus contains proteins that are similar to those in the nerve cell insulator. Once the body launches an attack on the viral protein, in other words, it also targets the myelin.
It's possible that researchers may one day find a single virus is linked to the development of MS, experts say. But, "it may not be any particular virus," said Dr. James Miller, an associate professor of clinical neurology and director of the Multiple Sclerosis Center at New York Presbyterian Medical Center. "It may simply be the right confluence of what the immune system is doing when you get an infection."
Other researchers have linked MS to the common bacterium Chlamydia pneumoniae.
Healthy Adam: MS linked to common bacterium
Whatever the cause, as the immune system chews away at the myelin, electrical signals slow or become jumbled and MS sufferers develop deficits in both sensory and motor abilities.
But exercise can improve functionality, Miller said. Doctors need to remind MS sufferers that exercise is good for them because sometimes symptoms get worse right after exercise, he said. But this is just a transient effect.
Like most other autoimmune disorders, MS has a gender bias. Women are affected at a rate of two to three times that of men, though no one knows why. Some researchers have pointed to female hormones. But many experts believe this is too simplistic, especially since the disorder doesn't die down when women reach menopause and experience lower estrogen levels.
It's possible that this gender gap in susceptibility to autoimmune disorders may be related to the differences in the female immune system that allow women to carry a pregnancy, some scientists say.
"There are immunological hazards that women experience because they are made to have babies," said Dr. Alan Beer, professor of immunology and microbiology and obstetrics and gynecology at the University of Chicago Medical School.
A woman's immune system has to be able to accommodate the growing fetus, which is genetically dissimilar to her because half its chromosomes come from the father, Beer explains.
Pregnancy often results in a reduction of symptoms, according to the Chicago physician. Women with autoimmune disorders have high levels of T helper 1 (Th-1) cells, immune system soldiers that promote inflammation and mediate much of the myelin destruction. When women are pregnant, inflammation suppressing cells (Th-2s) become more abundant as the body tries to protect the pregnancy. This leads to an improvement in autoimmune symptoms, according to Beer.
Unfortunately, while pregnancy appears to protect women against disease flare-ups, there is some evidence to suggests that women with MS may be predisposed to attacks during the six months following delivery, according to the New York expert.
"Many women anguish over whether they should become pregnant fearing that this will exacerbate their symptoms," Miller said. "But it doesn't have a great impact on the overall course of the disease."
Still Miller says, women with MS contemplating pregnancy must realistically assess the severity of their disease. Because MS can impact your ability to raise children, "you need to be sure your relationship is stable enough to weather any difficulties caused by the disease," he adds.
Ultimately, scientists may come up with a solution to MS long before anyone completely understands what triggers the condition.
MODIFYING THE IMMUNE SYSTEM
University of Pennsylvania researchers have found a way to halt the disease in mice that have a similar condition to MS. Their approach is to modify the immune system while not completely turning it off.
Dr. A.M. Rostami, a professor of neurology and director of neuroimmunology, and colleagues noticed that when levels of the inflammatory protein "interluekin-12" rose, so did the number of Th-1 cells. They also observed that healthy mice injected with interluekin-12 developed MS-like symptoms.
Perhaps by lowering the amount of interluekin-12 in an animal's body, they reasoned, you could decrease the number of Th-1 cells and block further nerve damage.
Which is just what happened when they injected the mice with anti-interluekin-12 antibodies. "When we gave it to the mice we saw that the mice didn't have relapses," Rostami says. "And that suggests that our idea was right."
The therapy didn't knock out all the animals' Th-1 cells, which is important because these white blood cells are needed to fight certain kinds of infections, Rostami says.
With the animal studies behind them, Rostami and his colleagues are hoping to set up human trials soon.
Linda Carroll's work often appears on the New York Times Syndicate.