Gut Bacteria Affect Immune Function (Can this lead to systemic disorders?)

I blogged earlier about the role of gut bacteria in the development of obesity and pointed out that mice raised in a sterile environment (i.e. sterile gut as well) do not get obese even on a high fat diet yet when colonized with gut bacteria from obese mice these sterile thin mice become obese even with restricted dietary fat intake.

Now recent work from scientists at Cal Tech has shown that gut bacteria may also play an important role in regulation of inflammatory processes systemically including in the central nrevous system. These studies involved sterile mice which do not develop, or have a significantly attenuated form of, experimental autoimmune encephalomyelitis (EAE) which is an animal model of multiple sclerosis, MS. MS is a progressively degenerative disease that results in the deterioration of the protective fatty myelin sheath surrounding nerve cells. The loss of myelin impairs the processes of communication between nerve cells. This loss of neural interaction leads to a host of symptoms including loss of sensation, muscle spasms and weakness, fatigue, and pain. Although the exact cause of MS is not known, what is known is that viral and bacterial infections result in an increase in MS symptoms in afflicted individuals.  When sterile mice were inoculated with Bacteroides fragilis, a bacteria from a group known as segmented filamentous bacteria (these bacteria are known to cause intestinal inflammation) they developed MS.

Thus, it seems that one is, or becomes, what one eats. The potential health benefits from research such as this is that some day the ingestion of certain forms of probiotic bacteria may be included in the regimen of fighting off and/or treating a variety of immune-related disorders.

Proc Natl Acad Sci U S A. 2011 Mar 15;108 Suppl 1:4615-22. Epub 2010 Jul 26.

Proinflammatory T-cell responses to gut microbiota promote experimental autoimmune encephalomyelitis.

Lee YK, Menezes JS, Umesaki Y, Mazmanian SK.

Science. 2010 Dec 24;330(6012):1768-73.

Has the microbiota played a critical role in the evolution of the adaptive immune system?

Lee YK, Mazmanian SK.


  1. That is very interesting. It raises questions about gastrointestinal flora. For instance, is a bad bacteria always bad? Is Bacteroides fragilis all bad or just bad in certain amounts or conditions, or just for certain people? Recently researchers have found that H.pylori infection, which is known to increase risk of peptic ulcer and gastric adenocarcinoma, may actually have a protective effect against inflammatory bowel disease.(See Gut doi:10.1136/gut.2010.220087)

  2. Bacteroides fragilis cannot be considered bad under all circumstances since this bacterium is a key contributor to immune homeostasis in the gut, which is an important part of continued surveilance for pathogens in the GI. However, there are toxin-producing strains of B. fragilis, termed enterotoxigenic Bacteroides fragilis (ETBF) and these strains are an established cause of diarrheal disease in people. Thus, it is a combination of strain and likely amount as well as local gut environment that determines "good" or "bad" actions of Bacteroides


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