A healthy gut is a crowded but happy place, with trillions of microbes pitching in to help digestion and immunity. But if the relationship sours, the results can be painful, even dangerous. HSPH immunologists are zeroing in on how certain microbes can trigger—and others relieve—one such disorder, inflammatory bowel disease.
IBD results from a loss of homeostasis, or balance, between the immune system and the microbes that inhabit the intestine. Research led by HSPH immunologists Laurie Glimcher and Wendy Garrett identified two microbes that can trigger IBD and a functional food containing several species that appears to counteract them by changing the gut environment.
“We identified two microbes that instigate gut inflammation that leads to inflammatory bowel disease in mice,” said Garrett, HSPH assistant professor of immunology and infectious diseases and HMS instructor in medicine at Brigham and Women’s Hospital. Having identified these potentially harmful microbes, Klebsiella pneumoniae and Proteus mirabilis, the researchers then fed the mice a commercial brand of yogurt containing Bifidobacterium animalis lactis, a suspected probiotic, or beneficial microbe. (The yogurt maker, Danone, provided a gift to HSPH that helps to fund this research.)
The results were promising: symptoms of IBD decreased in mice that consumed B. animalis, and tests showed that consumption of the probiotic changed the environment of the mouse’s gut, rendering it inhospitable—possibly too acidic—for the harmful microbes to flourish. The findings shed light on a so-called functional food that has been widely promoted but not well understood.
The findings are reported in two studies, published in the Sept. 16 edition of Cell Host & Microbe and online Oct. 4 in Proceedings of the National Academy of Sciences.
IBD is a chronic inflammatory disorder that afflicts 1.4 million people in the United States, and the incidence is rising around the world. Not only is IBD a devastating and debilitating chronic illness, it is also one of the three highest risk factors for the development of colorectal cancer. There are two principal forms of IBD: Crohn’s disease and ulcerative colitis. Approximately 30,000 new IBD cases are diagnosed each year in this country.
“Whether IBD is caused by individual species of bacteria or disruptions of entire microbial communities remains controversial,” said Laurie Glimcher, the Irene Heinz Given Professor of Immunology at HSPH and an HMS professor of medicine at BWH.
According to Garrett, “the findings of these two publications suggest that answer bridges both hypotheses—specific species of bacteria appear to work in concert with the indigenous gut microbial community to cause IBD, and functional foods may alter gut microbial communities to restore health.”
For more information, students may contact Wendy Garrett at wgarrett@hsph.harvard.edu.
Funding Sources: The National Institutes of Health, Danone Research and the Crohn’s and Colitis Foundation of America, plus career development awards from the Burroughs Wellcome Fund and the NIH; the authors are solely responsible for the content of this work.
Disclaimer: The researchers are unable to provide treatment recommendations for individual cases.
