Simply smelling seafood can make those who are allergic to it terribly ill, making them more prone to avoid it. People who get food illness after eating a specific meal demonstrate the same avoidance tendency.
Scientists have long known that the immune system plays an important part in human reactivity to allergens and pathogens in the environment, but it was unknown whether it also had a role in inducing these types of behaviors toward allergic stimuli.
According to Yale-led study published in the journal Nature, the immune system plays an important role in modifying human behavior.
We find immune recognition controls behavior, specifically defensive behaviors against toxins that are communicated first through antibodies and then to our brains.
Ruslan Medzhitov
“We find immune recognition controls behavior, specifically defensive behaviors against toxins that are communicated first through antibodies and then to our brains,” said Ruslan Medzhitov, Sterling Professor of Immunobiology at Yale School of Medicine, investigator for the Howard Hughes Medical Institute, and senior author of the study.
According to the study, without immune system communication, the brain does not notify the body of potential environmental dangers and does not attempt to avoid those threats.
A team in the Medzhitov lab, led by Esther Florsheim, a postdoctoral researcher at Yale who is now an assistant professor at Arizona State University, and Nathaniel Bachtel, a graduate student at the School of Medicine, studied mice that had been sensitized to have allergic reactions to ova, a protein found in chicken eggs. As expected, these mice avoided water laced with ova, but control mice preferred ova-laced water sources. They discovered that sensitized mice developed an aversion to ova-laced water sources that lasted for months.
The team then examined whether they could alter the behavior of sensitized mice by manipulating immune system variables. They found, for instance, that mice allergic to ova lost their aversion to the protein in their water if Immunoglobulin E (IgE) antibodies, produced by the immune system, were blocked.
IgE antibodies cause the release of mast cells, a type of white blood cell that, along with other immune system proteins, communicates with brain regions that drive aversion behavior. Without IgE as an initiator, information transmission was halted, and mice no longer avoided the allergen.
According to Medzhitov, the findings demonstrate how the immune system developed to assist animals escape harmful ecological niches. Understanding how the immune system remembers prospective threats, he noted, could one day aid in the suppression of excessive reactivity to many allergens and other diseases.
