Over Cleanliness May be ‘Bad’ for Kids’ Immune System

The prevalence of antibiotics and anti-bacterials together with modern hygiene has significantly reduced the number of microbes we are exposed to.  It is thought that our immune system is supposed to develop by encountering microbes, so being too clean throws it out of whack as the immune system overreacts to minor attacks. Proponents of the ‘hygiene hypothesis’ have always thought that there is a correlation between the reduced amount of microbes we are exposed to and the rise in the rate of autoimmune diseases.

A recent study published in Nature found that mice raised germ-free are likely to have a more severe case of asthma and ulcerative colitis (a common form of inflammatory bowel disease), when compared to those raised under normal laboratory conditions. The researchers have identified a mechanism in mice that may explain the role of exposure to microbes in the development of asthma and inflammatory bowel disease.

The research shows that in mice, exposure to microbes in early life can reduce the body’s inventory of invariant natural killer T (iNKT) cells. The iNKT cells help to fight infection but can also turn on the body, causing a range of disorders such as asthma or inflammatory bowel disease.

The researchers induced two groups of mice to develop forms of asthma or ulcerative colitis. The two groups of mice are: the germ-free (GF) mice, which are raised in a sterile environment, and the specific-pathogen-free mice raised under normal laboratory conditions. GF mice had more iNKT cells in their lungs and developed more severe disease symptoms, indicating that exposure to microbes was somehow influencing iNKT cell levels and making the GF mice more susceptible to inflammatory diseases. The study also found that a lack of exposure in early life could not be compensated for by introducing the GF mice to a broader range of microbes in adulthood indicating that the age of exposure is also important.

Although the study provides evidence to support the hygiene hypothesis, it should be noted that human children cannot live in an environment as germ-free as mice in a sterile lab. So it is not yet clear if this effect will be the same to real children in our world.







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