A new study finds that adults who are allergic to shrimp tend to have a less intense immune-system reaction to the shellfish compared with children - raising the possibility that some allergy sufferers build up a tolerance to shrimp as they grow older.

Allergies to shellfish, such as shrimp, lobster and clams, are among the most common type of food allergy. Reactions can range from mild symptoms, like nasal congestion and hives, to serious or even life-threatening problems, including severe airway constriction and a sudden, sharp drop in blood pressure.

Shellfish allergies also tend to be long-lasting, often persisting into adulthood. But little has been known about how children and adults might differ in the immune response to shrimp proteins.

In the new study, reported in the Journal of Allergy and Clinical Immunology, researchers looked at this question using blood samples from 34 children and 19 adults with a history of allergic reaction to shrimp.

They found that among children, blood levels of IgE antibodies against shrimp were typically four times higher compared with adults. The children’s antibodies also tended to bind to more shrimp proteins, and to bind to those proteins more strongly.

The findings are the first to show that children tend to have a stronger immune-system sensitization to shrimp than adults, according to the researchers, led by Dr. Rosalia Ayuso of Mount Sinai School of Medicine in New York.

The researchers note that the study did not follow participants over time, and it’s not known at what age they first became sensitized to shrimp. So it is unclear whether the adults were sensitized in childhood and then gradually had a reduction in their shrimp antibodies.

However, the findings do suggest that allergic reactions to shrimp may wane with age, according to Ayuso’s team.

And that, the researchers say, means that it may be worthwhile for adults with a history of shrimp allergy to undergo objective testing, with a food challenge, to see whether they have built up a tolerance.

Food challenges - where an allergy patient consumes the suspect food under medical supervision to see if it triggers a reaction - are considered the “gold standard” for diagnosing food allergies.

There are other tests as well - the skin-prick tests and antibody blood tests - but they are not always an accurate measure of whether a food will trigger a physical reaction. In one recent study, Ayuso’s team notes, half of participants with either a history of reactions to shrimp or positive results on skin-prick or blood testing were able to eat shrimp proteins without a problem during a food challenge.

SOURCE:

Journal of Allergy and Clinical Immunology, online May 14, 2010.