Study: Cats Ok for Asthmatic Kids

(HealthScout) -- Cat lovers can breathe easier, thanks to a new study showing that the felines aren't necessarily in the doghouse when it comes to causing asthma.

Virginia scientists say children exposed to cat dander can develop an immune response to the allergen without having breathing symptoms. The finding, reported in the March 10 issue of The Lancet, challenges the conventional wisdom that children with asthma should live in cat-free homes, says Dr. Thomas Platts-Mills, head of the Asthma and Allergic Diseases Center at the University of Virginia in Charlottesville.

"The implication is clearly that we do not recommend avoiding cats as a method of primary prevention," Platts-Mills says. On the other hand, he adds, "I don't recommend keeping cats in a community as a method of primary prevention" of asthma.

Cats are an enigma to asthma researchers. They are a major source of irritants -- generating 10 to 100 times more allergens than dust mites -- and their dander stays afloat in the air for a long time, exacerbating exposure.

Yet several studies have shown that people who live with cats are often less sensitive to the animals and less likely to suffer bouts of asthma. And while some 30 percent of American children are prime candidates for cat allergies, only about 10 percent wind up with them.

Why that's true hasn't been clear until now.

In the latest work, Platts-Mills and his colleagues studied 226 boys and girls in the seventh- and eighth-graders, 46 of whom had symptoms of asthma and hypersensitive airways. The children filled out questionnaires about the allergens they were exposed to at home and underwent blood and skin tests to measure their reactions to a variety of irritants.

Building a tolerance

Although contact with cats was a predictor of asthma, children exposed to high levels of dust mites were up to four times as likely to suffer breathing attacks, the researchers found. Moreover, those with the most contact with cat allergens appeared to be less instead of more sensitive to the animals.

"Many of the children who live in a house with a cat have become tolerant to the cat," Platts-Mills says. "The mechanism is an immune response which is like allergy but is modified. It doesn't cause the disease but the underlying [immunologic] event."

Typically, allergens like one called Fel d 1 in cat dander spark a two-stage reaction in sensitive people known as a Th2 response. The first half produces immune proteins called IgG and IgG4, followed by IgE, which triggers symptoms like sneezing and wheezing.

But Platts-Mills and his colleagues found that some children exposed to high amounts of cat dander had a modified Th2 response, one which involved IgG and IgG4 but not IgE, and thus no asthma.

Platts-Mills says it's not clear whether a similar reaction occurs with exposure to other allergens, though he suspects dogs would also prompt a modified Th2 response. That dust mites do not is likely because their principal allergen is an enzyme that prompts a different kind of immune response.

A related reaction, the Th1 response, has been the target of conventional allergy therapy, especially in Europe, where scientists have been experimenting with a tuberculosis vaccine as a way to prevent allergies. Yet Platts-Mills says researchers should rethink this strategy in light of the new findings. "We think [modified Th2] is the really the target for allergy shots," he says.

Dr. Scott Schroeder, an asthma specialist at Montefiore Medical Center in the Bronx, says the latest work "is interesting because it sort of makes us rethink how the immune system is stimulated."

"There are so many things we don't know about what we eat and the things we are exposed to," Schroeder says. He adds that asthma rates have soared in industrialized nations, but not in underdeveloped ones.

About 15 million Americans have asthma.

If you're attached to your kitty, you might not have to give it up.

To learn more about asthma and ways to help prevent flare-ups, visit the American Academy of Allergy, Asthma & Immunology.

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