From the intestinal samples, Bailey's team could determine the relative proportion of at least 30 types of bacteria residing there.
Compared to the control mice, the stressed animals showed two marked differences: The proportion of one important type of bacteria in the gut Bacteroides fell by 20 to 25 percent while another type Clostridium increased a similar amount. Also, levels of the two biomarkers, IL-6 and MCP-1, jumped 10-fold in the stressed mice, compared to controls.
The researchers then treated stressed mice with broad-spectrum antibiotics that could kill as much as 90 percent of the intestinal bacteria for a short period. When they again looked at the two immune biomarkers in the stressed mice, they saw only a doubling of IL-6 and MCP-1 an increase only one-fifth as much.
"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. "That showed that the bacteria are involved in the ability of stress to prime the innate immune system."
He said that the research shows that some of the changes in systemic immunity in the body can be influenced by changes in these bacterial colonies, a result that reinforces the idea that they have a broader effect on the immune response.
The next step, the researchers say, is to better understand the roles that the bacteria play in activating the immune system, and to determine if other factors are playing a key role in the process.
|Contact: Michael Bailey|
Ohio State University