I met my two-month-old niece for the first time over the holiday break. I flew out to Eugene, Oregon, hastily hugged my sister, took little Vi straight from my brother-in-law’s arms, and proceeded to explain to her the ins-and-outs of infant first aid and CPR. I thought she might be comforted knowing that if she ever chewed off the eye of her favorite chicken toy, choked on it to the point where she lost consciousness and her heart stopped beating, I would know what to do.
She stared back at me from this perfect little face, so serious, but it wasn’t comfort I saw there. I have a feeling that the face she was giving me is one that I’ll come to know as her “Who Is This Ridiculous Person and Why Is She Wasting My Time” look. For now, however, I’m going to pretend that it’s her “I’m Riveted By All You’re Telling Me” look. And so we had lots of science-y talks, Vi and me, over the next ten days.
Her favorite discussion was about the biodiversity hypothesis, specifically work reported by Hanski et al. in the Proceedings of the National Academy of Sciences (PNAS). The biodiversity hypothesis is built around two observations: (1) that by 2050, two-thirds of humans are expected to be urbanites surrounded by bricks and pavement and little green space and (2) that the occurrence of allergies and autoimmune diseases among city-dwellers is rising. Scientists hypothesize that, when taken together, these two pieces of information suggest that exposure to the outdoors, biodiversity, and environmental microbes, is necessary for adequate stimulation of the immune system. When these things are limited i.e. when contact with the natural world doesn’t take place regularly, then chronic inflammatory diseases like allergies are more likely to develop.
Vi and I were in an appropriate place for this discussion. We were on the coast, walking past Haystack Rock (made famous in the movie The Goonies) on Cannon Beach, and although she was bundled against the light mist of a rain that was hanging on the air, she was still wide eyed and taking it all in—the water, the mounds of tubular weeds, the sand dollars I wiggled around in front of her face.
But Vi wasn’t a newbie to the world outside the crisp white walls of her parents’ townhouse. At five-days-old, she visited the beach at Washburne Memorial State Park for the first time; at a couple of weeks old, she was strapped to her mother’s chest for a hike on Mt. Pisgah; in early December, she helped scour a Christmas tree farm for the perfect specimen; and on most days, little Vi gets strolled around various parks in Eugene.
Hanski et al. would say that my sister and brother-in-law should continue to expose their daughter to forests and flowers and everything good and green; either that or move her to the country, because in their new work, these Finnish scientists show that the healthiest children in eastern Finland are the ones that live surrounded by environmental biodiversity, especially forest and farmland. These children carry the greatest diversity of Gammaproteobacteria (commonly found in soil and on plants) on their skin. In contrast, atopic children (those with an allergic disposition) more commonly live in built environments or, curiously, near water, and their commensal skin bacteria are less diverse. In addition, Hanski et al. show that the abundance of Acinetobacter (a genus of Gammaproteobacteria) on the skin of healthy kids is linked to increased production of IL-10, an anti-inflammatory cytokine and allergy-protectant.
The connections between biodiversity, human commensal microbes, and the immune system are wildly complex, and many questions remain, including: what is the mechanism by which Gammaproteobacteria influence the expression of IL-10? And how exactly do environmental microbes affect the diversity and community structure of commensal skin microbes? Despite these mysteries, the implications of this study are clearly far reaching, extending beyond simple public health issues to how we build our built environments, how we view and protect wild lands, where we choose to live and work, and how we raise our kids.
For me, this study is just one more reason to feel good about encouraging my niece to play in the dirt, climb trees, and run through cornfields. And chances are, I’ll be right there too, engaging with Nature and getting my dose of environmental microbes.
For the details: Hanski, I. et al. 2012. Environmental biodiversity, human microbiota, and allergy are interrelated. Proc. Natl. Acad. Sci. USA, 109: 8334-8339.