When a nut allergy comes back

People with a peanut allergy can sometimes overcome their disease by eating trace amounts of peanuts. That may seem like a terrible idea for someone with an allergy to the food. But recent research has shown that for some people, it makes their allergy fade. Now comes some disappointing news for those undergoing this therapy: In most people, the treatment’s benefits last only as long as it’s continued. That means when people with a peanut allergy stop eating the food for a while, their next encounter with it will likely trigger an allergic reaction.

Peanuts are one of the leading triggers for a food allergy. But under a doctor’s supervision, eating small amounts of peanuts daily — and slowly increasing that amount — can cause the allergy to fade. Some doctors decided to see how permanent the effect was.

They treated 20 people with peanut allergies, slowly giving them increasing amounts of the very food that had caused their potentially life-threatening problems. After two years of treatments, each person could eat a dual package of Reese’s Peanut Butter Cups without developing an allergic reaction. Then the doctors stopped administering the peanuts for several months. When their patients later ate some peanuts, the allergy returned in nearly all of them. The findings appear in the February Journal of Allergy and Clinical Immunology.

An allergic reaction occurs when a person’s immune system overreacts to a food or other substance. And a peanut allergy is no small matter. At its mildest, it can cause stomach aches, itchy skin or other symptoms. At its worst, it can cause someone’s throat to swell up and close. Such a reaction can result in death. That’s why scientists and doctors are eager to find a way to keep a peanut allergy under control.

Kari Nadeau, an immunologist at Stanford University School of Medicine in California, led the new study. Twenty-three people with peanut allergies started the study. Eventually, three dropped out.

The 20 remaining patients consumed a powder made from peanut proteins. In the beginning, these volunteers ate only 1 milligram (a supersmall fraction of a peanut) per day. Still these molecules initially set off an allergic reaction. But after two years of this therapy, the recruits were downing 4,000 mg (about 1 teaspoon) daily. And now each could safely eat a handful of nuts without having an allergic reaction.

Then, doctors stopped the peanut therapy for three months. After the break, people again ate the peanuts (always under a doctor’s supervision.) Seven showed no effects. Thirteen, however, reacted — their allergy was back. Three months after this, the seven who had been fine again tried to eat peanuts. Four suffered a reaction. The rest — just three — could still eat peanuts 6 months after their therapy had ended.

Doctors running the study also compared blood samples from their volunteers with blood from other people with a peanut allergy. People who had been treated in the study had higher levels of immune cells known as regulatory T cells, or T-regs. These cells help calm the immune system when a person eats peanuts. The seven people who remained allergy-free after the three-month break from eating peanuts had the highest levels of T-regs when tested at the two-year mark of the study. This indicates the therapy works by helping people make more of the calming cells.

Eating small amounts of peanuts under supervision is the best way to treat this allergy, physician Calman Prussin told Science News. However, he adds, the new study shows the benefits don’t last in most people. Prussin, with the National Institute of Allergy and Infectious Diseases in Bethesda, Md., did not work on the new study.

But the new study provides evidence that boosting T-reg production “is a good idea” in allergic patients, he notes. A goal for future treatment might be to find a way to keep T-reg levels up for longer stretches.

Power Words

allergy  The inappropriate reaction by the body’s immune system to a normally harmless substance. Untreated, a particularly severe reaction can lead to death.

cell  The smallest structural and functional unit of an organism. It is typically too small to see with the naked eye.

immune system  The collection of cells and their responses that help the body fight off infection.

infectious  A germ that can be transmitted to people, animals or other living things.

proteins  Compounds made from one or more long chains of amino acids. Proteins are an essential part of all living organisms. They form the basis of living cells, muscle and tissues; they also do the work inside of cells. Among well-known, stand-alone proteins: the hemoglobin in blood and the antibodies that attempt to fight infections.

T cells  A family of white blood cells, also known as lymphocytes, that are primary actors in the immune system. They fight disease and can help the body deal with harmful substances.