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article imageIs exposure to 'dirt' good for children?

By Tim Sandle     Mar 25, 2012 in Health
It has often been thought that exposing children to germs at an early age to build immunity makes sense and makes for healthier adults. Now some recent research into the immune systems of mice offers weight to this theory: dirt might be good.
It is perhaps something many parents are aware of, and it certainly gives some weight to the old wives and husbands tale, but exposure to non-pathogenic microorganisms at an early age leads to a more developed immune system.
The theory (often called the "hygiene hypothesis") runs that the human immune system is significantly influenced and shaped by exposure to microbes throughout life, in fact, it may be essential for the development of a normal immune system. Studies of disease patterns (epidemiology) indicates that early-life exposure to bacteria is related to preventing certain immune diseases. Such diseases include asthma and ulcerative colitis, a type of inflammatory bowel disease.
Confirmation that this old adage may be correct comes with the publication of some research undertaken by the Harvard Medical School, led by Dennis L. Kasper, MD, in the journal Science. The researchers undertook their studies on mice. They were specifically interested in the autoimmune diseases asthma and colitis.
The research revealed that early-life microbe exposure decreases the number of inflammatory immune cells in the lungs and colon, lowering susceptibility to asthma and inflammatory bowel diseases later in life.
One of the researchers, Richard S. Blumberg, is quoted by the Brigham Women's Hospital, as saying about the findings "These studies show the critical importance of proper immune conditioning by microbes during the earliest periods of life. Also now knowing a potential mechanism will allow scientists to potentially identify the microbial factors important in determining protection from allergic and autoimmune diseases later in life."
The findings may correlate with data which suggests that asthma and colitis are on the increase in countries where antibiotics -have been overused.
The researchers examined the susceptibility to both diseases in 'germ free' mice (which had been bred in special conditions) and normal lab mice. What they found out was that the germ free mice were very susceptible to both diseases, whereas mice exposed to 'normal' conditions were fairly resistant to both diseases.
Later in the study, the researchers attempted to reverse the effect by exposing the germ-free mice to the same microbes which the 'normal' mice had been exposed to. The result was that nothing changed, and the mice, which had been bred as germ-free, remained susceptible to both diseases. However, the researchers then went onto expose germ-free pregnant females, just before they gave birth birth, and discovered that their children (pups) were protected against the diseases.
At the cellular level, the researcher found that the normal mice had far lower levels of what are called natural killer T (NKT) cells in their blood stream compared to the germ-free mice. This suggests that the high NKT counts were at the root of their high susceptibility. It could be that bacteria block the production of NKT cells in young mammals.
Although the research is interesting and might, in the longer-term, prove the “hygiene hypothesis", a much wider series of studies would be required before the theory can be extended to people with any strong certainty.
The reference for the research paper is:
T. Olszak et al., “Microbial exposure during early life has persistent effects on natural killer T cell function,” Science, 2012.
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