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Prenatal Microbe Exposure Protects Against Asthma

Supports the 'hygiene hypothesis,' that lack of exposure explains increasing allergy prevalence

TUESDAY, Dec. 8 (HealthDay News) -- Prenatal exposure to environmental microbes protects the offspring from developing asthma, supporting the "hygiene hypothesis," or the idea that the increasing prevalence of allergies and asthma is due to decreasing exposure to environmental microbes, according to a study published online Dec. 7 in the Journal of Experimental Medicine.

To investigate the hygiene hypothesis, Melanie L. Conrad, Ph.D., from Philipps-University of Marburg in Germany, and colleagues exposed pregnant mice intranasally to the cowshed-derived bacterium Acinetobacter lwoffii F78.

The researchers found that maternal exposure to A. lwoffii F78 protected the offspring from developing asthma. The microbe caused a transient increase in lung and serum proinflammatory cytokine production and an increase in microbe-sensing Toll-like receptors (TLRs) in the lungs of the mother, while suppressing TLRs in the placenta. In contrast, exposure of pregnant mice lacking several TLRs to A. lwoffii F78 did not protect the offspring against asthma and no inflammatory response was present.

"These data establish a direct relationship between maternal bacterial exposures, functional maternal TLR signaling, and asthma protection in the progeny," Conrad and colleagues conclude.

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