WASHINGTON (Dispatches)-Men are much less likely to get multiple sclerosis (MS) than women because they are protected by high levels of testosterone, Scientists report.
 Scientists have now discovered how it works. Using a mouse model of MS, they have identified a guardian molecule -- triggered by testosterone -- that appears to protect males from disease. When female mice with disease are treated with this protective molecule, their symptoms were eliminated, reports a new study from Northwestern Medicine.
"This suggests a mechanism for the reduced incidence of multiple sclerosis and other autoimmune diseases in males compared to females," said lead study author Melissa Brown, professor of microbiology/immunology at Northwestern University Feinberg School of Medicine. "These findings could lead to an entirely new kind of therapy for MS, which we greatly need."
Women have three-to-four times the incidence of MS compared to men and the lower incidence in males is related, in part, to higher levels of testosterone. But until now, scientists haven't understood how the hormone provides protection. The new study discovered how testosterone does it, and how females can glean the benefits.
The discovery stemmed from an earlier lucky mistake in the lab in which male mice were used instead of female mice, because a graduate student hadn't yet learned to identify the nearly imperceptible genitals of male mouse pups.
Northwestern scientists showed that testosterone caused mast cells, a type of immune cell, to produce the guardian molecule, cytokine IL-33, in male mice. The guardian molecule triggers a cascade of chemicals that prevents the development of another type of immune cell, so-called Th17 cells that can directly attack the myelin.
"Because testosterone levels are seven-to-eight times lower in adult women compared to men, we speculate there are insufficient levels in females to activate this protective pathway," Brown said. "But we showed we can activate the pathway with the guardian molecule, IL-33."