Asthma is common in first world nations, unheard of in the developing world and rising quickly in countries making the transition.
Many theories have been posited to explain this association. They range from the idea that clean living somehow revs-up the immune system to a belief that swimming pool chemicals bring on the allergy-mediated condition.
The common denominator is that environmentally mediated phenomena associated with economic development are directly triggering asthma.
Shadmehr Demehri and colleagues at Washington University in St. Louis have postulated an indirect link, in which environmental factors trigger eczema, a benign though annoying skin condition, and the distressed skin cells create chemical signals that in turn trigger asthma.
Eczema is also linked to economic development. Nearly 17% of US children have it, and nearly 70% of children with eczema develop asthma, even though the prevalence of the letter condition in the general population is only 4-8%.
Demehri’s team believes the culprit is thymic stromal lymphopoietin (TSLP), an immune-stimulating molecule released by skin cells when they are damaged, as by eczema. TSLP, they theorize, causes lung tissue to over-react to allergens, which leads to asthma.
The team wrote-up the results of 3 experiments in the Public Library of Science Biology that provide support for its hypothesis.
First, the scientists showed that mice genetically engineered to develop eczema were prone to develop asthma. Then they deleted the gene coding for the TSLP receptor in the bronchial tissue of such mice and voila, the new editions did not develop asthma.
In the third step, the scientists created mice that over-produced TSLP in the absence of skin problems. These mice wheezed up the wazoo.
Case closed, at least in mice. Eczema is easily treated, by the way, with low-dose topical steroids.