Features

Michael Glenwood

Asthma's Inner World (continued)

The big question, though, is what the findings mean. To date, researchers have been charting the organisms that make up the microbiota, says Jonathan Braun, MD, PhD, a professor of Pathology at the UCLA School of Medicine whose research involves the microbiome. Now, he says, “we’re moving from cartography of the microbiome, finding out what [microbes] are in there, to finding out what do they do and what to do about it, what parts are useful and what parts are scary.”

Scientists might exploit such knowledge to develop microbiome-based diagnostic tools or microbiome-targeted therapies. Braun envisions, for instance, a home test kit that measures the metabolic products of a person’s gut microbiota. The results might be used to help consumers adjust their diet to reduce their risk of certain diseases.

But some scientists caution that we are not there yet and that it’s important not to oversell the microbiome. “I think it is very likely that microbiomes are involved in an incredible diversity of host phenotypes—including health, disease, etc.,” says Jonathan Eisen, PhD, a professor of Medical Microbiology and Immunology at UC Davis. “I also think largely because microbiomes are the hot thing, that there is a massive amount of overselling.”

Microbiome studies by Marsha Wills-Karp and others make it increasingly clear that we move through this world in congress with trillions of microbial companions—in our intestines, on our skin, in our eyes, and on every surface of the human body.

Seeking Asthma’s Switch

Wills-Karp’s interest in asthma grew out of research she conducted in 1986 as a postdoc at Yale, where she studied the effects of aging on the muscles that control the lung’s blood vessels. A prominent theory at the time held that children with asthma outgrew the disease as their lungs matured. Wills-Karp and her colleagues set out to look for an “aging component” responsible for that effect. They never found one, but their studies piqued her interest in the immune system’s role in asthma.

That work led her to take a close look at the hygiene hypothesis, which posits that being exposed to a wide variety of microorganisms in childhood helps program the immune system, and that the hygienic Western lifestyle deprives children of this important driver of immune development.

“In the developed world, we’ve reduced microbial exposure in early life in children,” says Wills-Karp. The widespread use of antibiotics, a high rate of Caesarean section deliveries (which prevents the newborn from being exposed to the vaginal canal’s microbiota), a low rate of breast feeding, migration from rural areas to cities, and other factors that go along with economic development reduce the variety of microorganisms children encounter. Without a rich microbial “education,” the regulation of the immune system becomes skewed in a manner that makes it more sensitive to certain antigens, according to the hygiene hypothesis. This imbalance leads to a heightened risk for asthma and allergies, as well as autoimmune disease.

Indeed, as childhood has become less germy in the last 30 years, rates of asthma, type I diabetes, Crohn’s disease and certain other chronic illnesses have climbed. Zeroing in on asthma, Wills-Karp calls up on her computer screen a color-coded world map showing asthma prevalence. As the map’s colors reveal, rates vary dramatically from country to country. For instance, the United States, United Kingdom and Australia are colored fire red, the shade for countries in which more than 10 percent of the population has asthma. Russia and China, on the other hand, appear as pale green, signifying asthma prevalence of 2.5 percent or less.