The immune system plays a critical role in protecting human health. However, a recent study in mice shows that the immune system may influence behavior, too. Mice exposed to allergens – substances that trigger allergies – avoided those substances.

Researchers studied two groups of mice: one that was predisposed to egg allergy and one that was not. They exposed the two groups to water that contained ovalbumin, a protein in eggs that triggers allergic reactions.

They found that regions of the predisposed animals' brains that respond to unpleasant stimuli became active when they ingested allergens, causing them to avoid the ovalbumin-containing water. The mechanisms driving this behavior involved activation of IgE antibodies and mast cells (essential immune system components), which, in turn, triggered the activity of key immune-related molecules – cysteinyl leukotrienes and growth and differentiation factor-15 (GDF-15). Interestingly, the animals' avoidance behavior occurred before allergy-associated gut inflammation manifested.

Cysteinyl leukotrienes are pro-inflammatory lipid mediators produced by various immune cells, including mast cells, eosinophils, basophils, and macrophages. GDF-15 is a cytokine that increases in response to stress, infection, and inflammation. It increases in aging, suppressing immune responses.

These findings suggest that the immune system can shape behavior in response to allergens in mice, potentially protecting against harmful exposures. The immune system also influences behavior by inducing depressive symptoms during periods of acute or, alternatively, chronic inflammation. Learn more in this clip featuring Dr. Charles Raison.

• Read study abstract.