Mice exposed to normal bacteria of the GI tract (gut microbes) in their early life develop resistance against autoimmune disease, according to new research.

The study may also have uncovered reasons why females are at greater risk of autoimmune diseases such as multiple sclerosis, rheumatoid arthritis, and lupus compared to males.

Researchers from The Hospital for Sick Children (SickKids) found that when female mice at high risk of autoimmune (type 1) diabetes were exposed to normal gut bacteria from adult male mice, they were strongly protected against the disease.

In this type of mouse strain, more than 85 percent of females develop autoimmune diabetes due to strong genetic risk factors. In contrast, only 25 percent of the females developed the disease after they were given normal male gut microbes early in life.

"Our findings suggest potential strategies for using normal gut bacteria to block progression of insulin-dependent diabetes in kids who have high genetic risk," says principal investigator Dr. Jayne Danska, senior scientist in Genetics and Genome Biology at SickKids and Professor in the Departments of Immunology and Medical Biophysics at the University of Toronto.

A second unexpected finding was the effects of the gut microbe treatments on sex hormones. "We were surprised to see that when young female mice received normal gut microbes from adult males, their testosterone levels rose. We then showed that this hormone was essential for the gut microbe treatment to protect against the disease. It was completely unexpected to find that the sex of an animal determines aspects of their gut microbe composition, that these microbes affect sex hormone levels, and that the hormones in turn regulate an immune-mediated disease," says Dr. Danska.

The findings support the ``hygiene hypothesis,`` which suggests that the dramatic increase in autoimmune and inflammatory diseases over the past 50 years results from changes in our exposure to microbes.
Gut microbes are essential for normal development and training of the immune system, for extracting nutrients from our food, and for protecting us from some infectious diseases.

The study was recently published in the journal Science.