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WASHINGTON - Elizabeth White's first encounter with peanuts - a nibble of a peanut butter cracker at age 14 months - left the toddler gasping for breath. Within minutes, her airways were swelling shut.

Elizabeth White, 7, mixes peanut powder with a fruit roll-up before taking her daily dosage in Raleigh, N.C., Thursday, Dec. 21, 2006. A study at Duke University is trying to help children with peanut allergies tolerate at least a little exposure. [AP]

A mere fifth of a peanut was enough to trigger an allergic reaction.

So it was with trepidation that her parents enrolled Elizabeth, at 4 1/2, in a groundbreaking experiment: Could eating tiny amounts of the very foods that endanger them eventually train children's bodies to overcome severe food allergies?

It just may work, suggest preliminary results from a handful of youngsters allergic to peanuts or eggs ¡ª and who, after two years of treatment, seem protected enough that an accidental bite of the forbidden foods is no longer a huge threat.

"We're so lucky," says Carrie White, Elizabeth's mother.

Now 7, Elizabeth can safely tolerate the equivalent of seven peanuts. For the first time, the Raleigh, N.C., girl is allowed to go on playdates and to birthday parties without her parents first teaching the chaperones to use an EpiPen, a shot of epinephrine that can reverse a life-threatening reaction.

"Our whole worry level is really gone."

Don't try this experiment on your own, warns lead researcher Dr. A. Wesley Burks of Duke University Medical Center. Children in the study are closely monitored for the real risk of life-threatening reactions.

But if the work pans out - and larger studies are beginning - it would be a major advance in the quest to at least reduce severe food allergies that trigger 30,000 emergency-room visits and kill 150 people a year.

"I really think in five years there's going to be a treatment available for kids with food allergy," says Burks.

Millions of Americans suffer some degree of food allergy, including 1.5 million with peanut allergy, considered the most dangerous type. Even a whiff of the legume is enough to trigger a reaction in some patients.

Moreover, food allergies appear to be on the rise. Peanut allergy in particular is thought to have doubled among young children over the past decade, prompting schools to set up peanut-free cafeteria zones or ban peanut-containing products.

There's no way to avoid a reaction other than avoiding the food, something the new research aims to change.

Allergies to pollen and other environmental triggers often are treated with shots called immunotherapy. A series of injections containing small amounts of the allergen builds up patients' tolerance, reducing or even eliminating symptoms in many people.

Shots proved too dangerous for food allergy. So Burks and colleagues at Duke and the University of Arkansas developed an oral immunotherapy.

Here's how it worked: First, youngsters spent a day at the Duke hospital swallowing minuscule but increasing doses of either an egg powder or a defatted peanut flour, depending on their allergy. They started at 1/3,000th of a peanut or about 1/1,000th of an egg, increasing the amount until the child broke out in hives or had some other reaction.

Then the children were sent home with a daily dose just under that reactive amount. Every two weeks, the kids returned for a small dose increase until they reached the equivalent of a tenth of an egg or one peanut ¡ª a maintenance dose that they swallowed daily.

After two years, four of the seven youngsters in the egg pilot study could eat two scrambled eggs with no problem, and two more ate about as much before symptoms began, researchers report in the January edition of the Journal of Allergy and Clinical Immunology.

In the peanut pilot study, yet to be published, six of the children challenged so far could tolerate 15 peanuts, Burks says; Elizabeth's limit was seven.

"We thought it would make some difference. We're surprised about the amount of difference it made," says Burks. "From one peanut to 15 peanuts is basically a huge difference."

But will it last? These youngsters still take their daily maintenance dose, which Elizabeth's mother nicknamed "peanut medicine" so as not to confuse a child taught to avoid peanut products. No one knows if the protection will last if they stop that daily dose, notes Dr. Marshall Plaut of the National Institutes of Health, which has a Food Allergy Research Consortium that's closely tracking Burks' work.

The next step: Burks' team is beginning larger studies that randomly assign youngsters to take either dummy powders or the egg- or peanut-containing ones, seeking better evidence for the treatment.

He's also giving patients like Elizabeth larger doses, to try to increase their resistance to the allergens. Blood tests signal promise: People who tolerate higher doses in turn have lower blood levels of a compound called immunoglobulin-E that's key to immune cells' overreaction to allergens.

"Inducing tolerance is an attractive approach," says NIH's Plaut. But, "you don't go into this kind of a study lightly" because of the risks.

"It's not something we're ready for everybody to do yet," stressed Burks.