Eczema’s link to asthma

I suffers from both eczema and asthma. It would be a good news if the scientists find a cure to both of them.

Breathe easy

May 21st 2009
From The Economist print edition
Researchers discover how a skin disease may trigger a lung complaint

ONE of the prices humanity seems to pay for getting richer is the rise of asthma. This life-threatening, allergy-driven lung disease is common in wealthy countries, absent from poor ones and on the rise in those making the transition. But exactly what causes it is unknown.

A number of explanations have been proposed. These range from the idea that clean modern living makes the immune system over-reactive to random allergens to the thought that chemicals in swimming pools are responsible. What these ideas have in common is the suggestion that some environmental change which accompanies economic development is the cause. A group of researchers led by Shadmehr Demehri of Washington University, in St Louis, believe these explanations are looking in the wrong place. Asthma is not, they think, caused directly by environmental factors. Rather, the link is indirect. The direct cause is a chemical distress signal produced in skin that is damaged by another hazard of modern life: eczema.

Eczema is also on the rise in the industrialised world, in the same sorts of countries where asthma is a problem. Unlike asthma it is not dangerous, so people rarely worry about it. Nevertheless, 17% of children in America have it, and similarly high figures are found in Australia, Britain and New Zealand. What is particularly intriguing is that many people with eczema go on to develop asthma (in America the figure is 70%). That compares with an asthma prevalence of 4-8% in the general population. As they describe in Public Library of Science Biology, Dr Demehri and his colleagues now believe they know what causes this link.

The culprit is thymic stromal lymphopoietin (TSLP), a signalling molecule secreted by damaged skin cells which elicits a strong immune response from the body to fight off invaders. Dr Demehri and his team hypothesised that eczema-induced TSLP enters the bloodstream and, when it arrives at the lungs, sensitises them so that they react to allergens that would not previously have bothered them. In other words, they become asthmatic.

They tested their hypothesis in a series of experiments on mice. First, using genetic engineering, they created mice prone to the kind of skin defects found in eczema. These mice were, as they hoped, susceptible to asthma. Then they used additional engineering to delete the gene for the receptor molecule which picks up TSLP in the lungs. These mice no longer developed asthma. Thirdly, they engineered mice to produce high levels of TSLP in their skin in the absence of other skin problems. These mice also developed asthma.

Taken together these experiments indicate—at least in mice—that skin damage creates susceptibility to asthma by releasing TSLP. If that proves true in people, too, it suggests several ways asthma might be prevented. One is to take eczema seriously, and treat it early. The usual treatment is to apply steroids to the damaged skin, but there is evidence that some parents reject this treatment for their children. If a link between eczema and asthma were properly established, that reluctance would probably diminish. In the longer term, it might be possible to devise drugs that inhibit the production of TSLP or interfere with TSLP-receptor molecules in the lungs. Better still, though, would be to work out what aspect of modern life causes eczema.

One possible culprit related both to cleanliness and bathing is the widespread use of detergents. By degreasing the skin, modern detergents might lead to infection and inflammation. At the moment, that idea is just speculation. But the question is an itch that certainly needs a scratch.

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