An international team of researchers led by Harvard Medical School have discovered that the billions of bacteria lining our GI tracts have coevolved with us.
These bacteria, which are essential for a healthy immune system, are ultimately our evolutionary partners.
“For every cell in your body that is you, that contains your specific genetic information, there are approximately nine foreign bacterial cells, primarily in your digestive tract and even on your skin,” said Dennis Kasper, Harvard Medical School professor of microbiology and immunobiology and senior author on the paper. “From the viewpoint of cell count, every human being is ninety percent microbial. Now we’ve found that these bacteria, which we need for optimal health, are species specific.”
This study, the first to demonstrate that microbes are specific to their host species, also sheds light on the hygiene hypothesis.
According to this idea, living in increasingly hyper-hygienic environments might contribute to recent spikes in childhood allergies, as these beneficial host specific microbes are hindered by antibacterial home products and cleaning chemicals.
“This raises serious questions regarding our current overuse of antibiotics, as well as ultra-hygienic environments that many of us live in,” said Kasper. “If the bacteria within us is specific to us and necessary for normal immune system function, then it’s important to know if we are in fact losing these vital bacteria. Are we losing the bacteria we have coevolved with? If that is the case, then this is yet further evidence supporting the idea that the loss of good bacteria is partly to blame for the increased rates of autoimmunity that we are now seeing.”
Cell. 2012 Jun 22;149(7):1578-93. “Gut immune maturation depends on colonization with a host-specific microbiota.” Chung H, Pamp SJ, Hill JA, Surana NK, Edelman SM, Troy EB, Reading NC, Villablanca EJ, Wang S, Mora JR, Umesaki Y, Mathis D, Benoist C, Relman DA, Kasper DL. Channing Laboratory, Brigham and Women’s Hospital, Harvard Medical School, Department of Microbiology and Immunobiology, Harvard Medical School.
This work was funded by the Crohn’s and Colitis Foundation of America, the Danish Council for Independent Research, the National Institutes of Health, and by an NIH Director’s Pioneer Award.