We don't want to sound ungrateful for everything our immune system does for us, but as people suffering from food allergies can attest, it can be a little overzealous at times. Now, researchers at the University of Michigan have found a way to retrain the immune system to ignore allergens by developing a nasal spray that vaccinates against peanut allergies, with promising results in mouse tests.

The immune system's job is to identify threats to the body and fight them off, but it doesn't always pick the right targets. In some people, the immune system overreacts to the presence of proteins from things like nuts, dairy products, latex, bee stings or certain drugs, leading to allergic reactions that can, in the most extreme cases, be potentially fatal.

"Right now, the only FDA-approved way to address food allergy is to avoid the food or suppress allergic reactions after they have already started," says Jessica O'Konek, lead author of the new study. "Our goal is to use immunotherapy to change the immune system's response by developing a therapeutic vaccine for food allergies."

In a way, developing a vaccine for allergies requires the opposite approach to a vaccine against disease. In the latter case, the goal is to train the immune system to recognize the invaders and mount a more efficient defense next time. Vaccinating against allergens, on the other hand, requires teaching the immune system to ignore these harmless proteins.

Previous research into fighting allergies involved exposing people with peanut sensitivity to increasing doses of peanut flour, but that approach is only effective as long as people keep dosing themselves. Other immunotherapy techniques may work better, including a recent study that erased the immune system's memory response to allergens, essentially turning off the reaction.

In the new study, the team's experimental vaccine works by effectively misdirecting the immune system to fight off a more dangerous target than the allergen. The vaccine, delivered as a nasal spray of very fine droplets, is made up of peanut proteins mixed with nano-emulsion consisting of highly purified soybean oil, detergents and water.

In past research, nano-emulsion has been found to induce a strong infection-fighting immune response. It was thought that the immune system would prioritize this over allergens, and with enough doses it would eventually learn that peanuts pose no threat to the body. Although it invokes an immune response, the nano-emulsion itself is harmless, and it contains no soy proteins to avoid triggering or creating soy allergy reactions.

To test their creation, the researchers gave either the vaccine or a placebo to peanut-sensitive mice. Each animal was given three doses over two months, then exposed to peanuts two weeks after the final vaccination. On studying the symptoms and immune reactions of the mice, the scientists observed that the properly-vaccinated group were protected against a range of symptoms, from the mild itching and irritated eyes, right up to the more severe, like wheezing and shock.

"We're changing the way the immune cells respond upon exposure to allergens," says O'Konek. "By re-directing the immune responses, our vaccine not only suppresses the response but prevents the activation of cells that would initiate allergic reactions. Importantly, we can do this after allergy is established, which provides for potential therapy of allergies in humans."

As it stands, the researchers aren't sure how long this protection might last, but finding out is the goal of further study. If this works, human trials could eventually follow.

The research was published in the Journal of Allergy and Clinical Immunology, and the work was funded by the Food Allergy Research and Education organization.