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IS URBAN LIFE TOO HYGIENIC?

CHLDREN WHO grow up on dairy farms are considerably less likely to develop allergies or asthma than their urban counterparts. This finding, published in Science, September 4, 2015, offers new evidence for what’s known as the Hygiene Hypothesis, that modern cleanliness and the widespread use of antibiotics have rid the environment of microorganisms that once enhanced a growing child’s immune system. Succinctly, a sterile environment comes with risks of its own.

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As noted in “How Farm Life Prevents Asthma,” by Jocelyn Kaiser, “Some researchers suspect a key reason is that the kids breathe in air full of molecules from the cell walls of certain bacteria, called lipopolysaccharides for their fat-sugar structure.” Also known as endotoxins, in a sense these fragments of bacteria from cow manure and fodder teach the immune system not to overreact to foreign substances.

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Farm chores may provide an unexpected benefit: asthma prevention. Image from Science, September 4, 2015, Source/Corbis.

The research was done in Europe, at Belgium’s Ghent University, France’s Aix Marseille University, Germany’s Ludwig-Maximilians-Universität and the Netherlands’ Erasmus Medical Center. The paper “Farm Dust and Endotoxin Protect Against Allergy Through A20 Induction in Lung Epithelial Cells” by Martijn J. Schuijs et al describes experiments with mice exposed to low doses of endotoxin. The bacteria protected the mice from developing HDM (House Dust Mite)-induced asthma.

One of the researchers, pulmonologist Bart Lambrecht, noted that hitherto the Hygiene Hypothesis involved the immune system directly. However, he says, “It’s not happening in the immune system. It’s in the structural cells of the airway. We need this environmental exposure to cool down the epithelium [the thin surface lining of trachea, bronchi and lungs] so it knows what’s dangerous and not dangerous.”

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Human airway.

The Ghent team also tested bronchial cells from healthy people and found that endotoxin exposure had an effect similar to that with the mice. An enzyme produced by the epithelial cells called A20 seems to play a role in this, and it’s suggested that drugs boosting A20 activity could help protect children with family histories of asthma. It’s a delicate balance, however; large doses of endotoxins can promote asthma.

Other researchers suggest the Hygiene Hypothesis continues to hold secrets. For instance, drinking unprocessed milk seems to ward off childhood asthma, and this is unlikely to involve the lung epithelium. Another research goal would assess whether the protective response lasts from birth into adulthood.

This is a direction that the European team is currently planning. ds

© Dennis Simanaitis, SimanaitisSays.com, 2015

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