Stress is a gut check on the immune system

Researchers had a gut feeling that gastrointestinal bacteria are harmed by stress, which then weakens the entire immune system, but it took two biomarkers to help them prove it. First, here's the scoop on bacteria in your digestive tract: You have about 90 trillion of those little buggers, and recent research has shown that they play an important role in keeping the immune system prepared to attack infections. One researcher has long been curious about the role stress plays in the effectiveness of these bacteria.

"Since graduate school, I've been interested in how stress affects the bacteria naturally in our bodies," Ohio State University researcher Michael Bailey said in a news release. "Even though we've known that stress changes these bacteria, we didn't really understand what that meant or if there was any sort of biological function associated with effects on these bacteria."

So, what Bailey and colleagues did first was create a situation where there were a few really stressed out laboratory mice. They took some docile animals and put them in a cage with an aggressive mouse two hours a day for six days. They then took blood samples and analyzed them for two biomarkers that measure stress--a cytokine called interleukin-6 (IL-6) and a protein, MCP-1, which summons macrophages to the site of an infection. Compared to the control mice, the stressed animals showed that a couple of important kinds of bacteria in the gut fell by 20 to 25 percent each. The levels of the two biomarkers jumped 10-fold in the stressed mice. Then they treated the stressed mice with antibiotics that could kill as much as 90 percent of intestinal bacteria for a short period of time. Biomarkers in those mice only doubled.

"We know now that if we knock the population of bacteria down with antibiotics, we don't have the same innate immune response," Bailey said in the news release. "That showed that the bacteria are involved in the ability of stress to prime the innate immune system."

- read the release
- and a story at Psych Central