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article imageDiabetes in mice kept at bay by bacteria in their gut

By Bart B. Van Bockstaele     Sep 22, 2008 in Science
Naturally occurring bacteria help keep the immune system in check, and may help ward off auto-immune diseases such as type 1 diabetes.
Although most North Americans have hardly an inkling as to what "germs" are, they are thoroughly afraid of them. People all over the world are scratching their heads when they see excessive use of antibiotics that are even used for killing viruses in spite of the fact that viruses are not the least bit sensitive to them, anti-bacterial soaps, even anti-bacterial wipes for wiping one's bottom, disinfecting sprays, powders, whatever. That's not even counting the gut cleansing therapies sold for ridiculous prices by alternologists of all types to the naive and credulous. The prized colonic does nothing to cleanse your gut that it cannot do by itself. Worse, it is a dangerous procedure and can be the cause of many problems of which vitamin deficiencies are probably the least. Of course, after selling one the colonic, the "therapist" or health food store will happily supply one with a whole bunch of useless liquids and powders to restore the balance. They also don't work. In the end, they only thing thoroughly cleansed is one's wallet.
This "germophobia" is not doing people any good, and more than anything is it responsible for the emergence of bacteria that are resistant against antibiotics, something that is becoming a serious problem in society. This is especially visible in hospitals because that is where we find the highest concentrations of the most fragile and vulnerable people who need antibiotics the most and resistant bacteria the least.
What bacteriophobes either don't know or don't want to know, is that we are hosts to trillions of bacteria ourselves and that these germs don't harm us, on the contrary, they are part of what we are, and without them, our lives would be a lot less pleasant and quite a bit shorter. Although hard to verify for obvious reasons, some have estimated that up to 10% of our body weight could be made up of bacteria (see for example Dorion Sagan and Lynn Margulis in Garden of Microbial Delights). These bacteria live happily and harmlessly in our intestines, on our skin, and elsewhere. We call them the "microbiome". In other words, we need bacteria for our survival. In spite of people's aversion to germs, bacteria have become a hot study topic, and new discoveries are made all the time.
The effects of the microbiome has been linked to obesity and inflammatory bowel disease. Now, Nature reports that bacteria in the intestines of mice help these animals ward of type 1 diabetes.
Type 1 diabetes is on the rise in humans, especially in developed countries. The origins are as of yet unknown, although scientists have advanced many possible explanations, such as virus infections or chemicals in processed foods. "The problem is, we've never found out what that trigger is," says Denis Daneman. He is the chairman of paediatrics at the Hospital for Sick Children in Toronto, and he is currently investigating ways that diet may increase the risks.
More than a decade ago, some scientists discovered that a strain of mice prone to diabetes, is even more likely to get the conditions when it is grown in a sterile, microbe-free environment. This suggested that the condition could possibly be avoided by exposure to bacteria.
Researchers decided to look at the interactions between the immune system and resident bacteria (bacteria living inside or on the skin of the mice). It was known that the protein MyD88 is an important regulator of these interactions. For this reason, they eliminated it. In spite of the fact that most mice of diabetes-prone strain eventually get the condition, none of the ones that lacked MyD88 got it. If, however, they were kept in a sterile environment, they still got it. Subsequent research has strengthened this evidence.
Researchers also discovered that loosing MyD88 led to a different composition of the bacteria in the intestines. The hypothesis is that MyD88 prevents the bacteria's prevention of diabetes to a certain degree. This hypothesis explains why MyD88 increases the risks in the presence of bacteria, and has no effect when no bacteria are present.
This hypothesis is nicely compatible with the hygiene hypothesis that suggests that if an organism encounters fewer microbes than evolution has led it to expect, this organism would be more likely to develop autoimmune diseases. The idea is that if you are exposed to a lot of pathogens, your immune system will become more powerful, while it will remain vulnerable if it is not exposed to as many bacteria. This would be evidence that supports the hypothesis that microbiota have much more influences than on digestion alone.
It needs to be stressed, however, that this is lab research in very controlled circumstances. It remains to be seen whether this can be translated to the real world and, mice and humans being different species, whether this can have consequences for people.
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