An estimated 400 million people worldwide suffer from hay fever, and 300 million have the associated condition of asthma, according to the first-ever global allergy impact report published in June by the World Allergy Organization. Allergies have become increasingly common during the last few decades, and experts expect the trend to continue.

Now a team of scientists says that a closer look at the avian immune system might help new and better allergy treatments take flight.

A key culprit in allergies is the antibody immunoglobulin E (IgE), a protein produced by the human immune system. Scientists believe that IgE evolved because it protected our ancestors against parasitic infections. But IgE can also goad the immune system to launch all-out war against innocuous substances like pollen and peanuts.

Instead of producing IgE, birds, reptiles and amphibians make an antibody called IgY. From a structural standpoint, IgY looks similar to IgE, and both are believed to have descended from a common ancestor. But, until recently, scientists did not know if these two antibodies behaved similarly.

In people with allergies, IgE binds white blood cells for long periods of time and instructs these cells to unleash chemicals such as histamines. This cascade of events triggered by IgE can cause anything from itchy eyes to life-threatening airway inflammation. A team from King's College London decided to find out whether IgY also has a similar propensity for sticking to white blood cells, so they took IgY from a chicken and measured its binding affinity.

They found that the bird antibody does not behave like IgE but does act more like human IgG, an antibody that binds loosely to white blood cells and does not cause allergic reactions. “We thought with that structure, you would always have tight binding, but IgY tells us that is not always the case,” says Brian Sutton, a professor at King's College and an author of the paper describing the research (J. Biol. Chem. 283, 16384–16390; 2008).

The next step, says co-author Rosy Calvert, is figuring out why the bird antibody has such a low binding affinity, because this might help scientists design therapeutic agents aimed at curbing the activity of IgE.

“We already have a therapy that shows that it's useful to block IgE from docking [onto white blood cells],” says Sarbjit Saini, an allergy and immunology expert at the Johns Hopkins University School of Medicine in Baltimore. “Could we also interfere with something that that allows IgE to stay bound?” Saini says. “By studying the IgY structure, you might be able to gain some insight.”