Asthma and Allergies: Sizing up a Suspected Cause

A group of researchers at the University of California, San Francisco, may be making headway in the fight against asthma.

Dr. Richard Locksley leads a small team at UCSF considering new approaches to asthma research. His program is funded by Marion and Herb Sandler, a philanthropist couple who have underwritten research on many diseases. But Marion Sandler herself has suffered from asthma most of her life. After 40 years of spraying steroids down her throat, she wondered why there have been so few advances in preventing or treating asthma. We can recognize asthma—and we diagnose it in more and more children every year—but we don’t even understand what causes the condition.

Locksley and his team may be on the heels of some answers.

A new suspect, found everywhere

Asthmatics can have great difficulty breathing when confronted with allergens, the organisms that provoke an allergic response. Locksley and his colleagues were struck by the idea that a wide range of organisms known to be highly allergenic—from various fungi and molds, to dust mites and cockroaches, to shrimp and other shellfish—all have a common compound called chitin (pronounced KI-tin). They wondered, could the body’s inflammatory response to chitin be a root cause of asthma?

The team’s recent study, performed on mice, showed that chitin triggered an allergic response in the lungs. Their observations may explain why there is higher incidence of asthma where there’s a known problem with mold or insects, and why reactions to shellfish are so common. The shells, cell walls and exoskeletons of these critters are made of chitin. Moreover, they may leave chitin behind as they molt.

The hygiene hypothesis

A popular theory of why we’ve seen dramatic increases in allergies is known as “the hygiene hypothesis.” As the theory goes, developed countries have cleaned up so much bacteria and vaccinated against so many microbes that our immune systems overreact when faced with allergens. If we still grew up in “dirty” environments, it’s been suggested, we wouldn’t have so much allergy and asthma.

The hygiene hypothesis and the chitin hypothesis cross paths in an interesting way. Though we often think of bacteria causing health problems, chitin may be naturally broken down by bacteria.

“There are all these funky ideas about asthma, such as if you grow up with a dog under the bed before you’re 6 months old, or if you grow up in a farm environment, you almost never get asthma,” Locksley further explains. “Because bacteria has an enzyme that breaks down chitin, one possibility is that there will be low chitin where there is a lot of bacteria.”

Clean house?

So what are we to do—live knee-deep in bacteria to prevent allergies and asthma?

“That’s a big question, and a loaded question since it’s tough to say, ‘Go out and get dirty!’ ” Locksley says with a laugh. “If there really is an association with chitin, maybe the response is not so much to worry about the bacteria in a household, but to worry about the chitin. One approach might be to develop ways to break down chitin in the environment.”

Amplifying his point, Locksley cites a compelling example of bacteria and chitin at play.

“The snow-crab industry is a big part of a seasonal industry up in Alaska and Canada,” he begins, emphasizing that the shells of crabs are a rich source of chitin. “College kids come in and they work in these crab processing plants. It’s the food industry, so the first thing they do is get all the bacteria out of the environment by using microbicides. Then you’ve got these kids in there pulverizing chitin shells for hours on end.

“The attack rate for new onset asthma in that industry is something like 25 to 28 percent per year,” he says. “It’s now a major cause of disability in Canada.”