As many as eight out of every 100 children in the U.S. suffer from food allergies, a rate that rose 18 percent between 1997 and 2007. Although some outgrow these reactions, many are plagued for life with symptoms that range from a tingling, itchy mouth to tightening airways and a potentially fatal drop in blood pressure.
Until now, the only way to prevent allergic reactions has been to avoid the offending foods, which can be difficult because traces of nuts, wheat and dairy lurk in many products. But a new study offers some of the best evidence that doing just the opposite—exposing patients to higher and higher doses of a food allergen—may help some overcome their sensitivity. In the largest placebo-controlled trial of its kind, Wesley Burks, a professor of pediatrics at the University of North Carolina at Chapel Hill School of Medicine, and his colleagues started 40 children with egg allergies on a dose of egg white powder equivalent to one ten-thousandth of an egg. The researchers, who published their findings in July in the New England Journal of Medicine, ramped up the dose, and after 22 months of therapy followed by a two-month break, 28 percent of the children were able to eat the equivalent of two and a half eggs. One year later 100 percent of those children were eating eggs and reporting no reactions. The approach, called oral immunotherapy, follows the same principle as shots for airborne allergens, although shots may be less safe for food allergies.
Researchers believe the treatment, which has also been tested for peanut and milk allergies, “teaches” the body to tolerate what it once rejected. Blood tests in children who responded to the trial showed decreased levels of the antibody IgE, which triggers the immune response, and increased levels of IgG4 antibodies, which discourage inflammation. Those who failed the egg tests may need a longer therapy period, Burks says, or they may be too sensitive to respond to therapy.
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A synthetic antibody might help those extrasensitive patients by binding (thus eliminating) free IgE in the blood. It is already approved for airborne allergies and is currently in trials for oral immunotherapy. Burks says, “The hope is that we can come up with a treatment in the next few years.”
FURTHER READINGS AND CITATIONSScientificAmerican.com/oct2012/advances