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Allergies linked to environmental diversity, human microbiota

Atopic individuals had less environmental biodiversity in the areas surrounding their homes — and less diverse skin bacteria — compared with healthy individuals, according to new study results.

Using atopic sensitization as a benchmark, researchers studied a random sample of 118 adolescents living in various population densities in a 15,000-square kilometer region in eastern Finland. Environmental biodiversity was measured as vegetation cover around the home along with the major land uses within 3 kilometers.

Participants were grouped as healthy or atopic based on IgE antibody level in a screen with Phadiatop, a mixture of common inhalant allergens. Skin bacterial flora was identified to the genus level from DNA samples from the volar surface of the forearm.

Generic diversity of proteobacteria was higher on the skin of individuals living in a more forested/agricultural land compared with individuals living in more developed areas and near bodies of water.

"Our study takes the 'hygiene hypothesis' out-of-doors, implying that exposure to environmental biodiversity, including environmental microbiota, perhaps especially in early childhood, is important for the development of the immune system," Research Professor Ilkka Hanski told Healio.com.

The important message for clinicians, according to Hanski, is "the strong association between the diversity of gammaproteobacteria in the skin microbiota and atopic sensitization."

"Causality from bacteria to atopy was furthermore supported by the correlation between the gammaproteobacterial genus /Acinetobacter /and the expression of interleukin(IL)-10 cytokine in peripheral blood mononuclear cells," Hanski told Healio.com.

Researchers noted that the study participants had lived in the same homes during their childhood years and thus were exposed to the same surrounding environment for a long time.

“Our results imply that gammaproteobacteria … may play a special role in the development and maintenance of the skin homeostasis and healthy barrier function, similar to that of certain gut bacteria,” the researchers wrote.

They concluded that interaction with natural environments in urban areas “may enrich the commensal microbiota and enhance its interaction with the immune system, with far-reaching consequences for public health.”