Study finds immune system can influence behaviour

Those who are allergic to seafood may feel quite ill just by smelling it, increasing their proclivity to avoid it. People who acquire food poisoning after eating a particular meal exhibit the same avoidance pattern.Scientists have long known that the immune system has a role in human sensitivity to allergens and diseases in the environment, but it was unknown whether it also played a role in producing these types of behaviours in response to allergic stimuli.

According to a Yale-led study published in the journal Nature, the immune system plays a critical role in modifying our behaviour.”We find immune recognition controls behaviour, specifically defensive behaviours 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.

Without immune system communication, the brain does not warn the body about potential dangers in the environment and does not try to avoid those threats, the study showed.
A team in the Medzhitov lab, led by Esther Florsheim, at the time a postdoctoral researcher at Yale and 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 tended to avoid water laced with ova, while control mice tended to prefer ova-laced water sources.The aversion to ova-laced water sources in sensitised mice lasted for months, they found.The team then examined whether they could alter the behaviour of sensitised 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 trigger the release of mast cells, a type of white blood cell that, along with other immune system proteins, plays a crucial role in communicating with areas of the brain that control aversion behaviour.

Without IgE as an initiator, the transmission of information was interrupted, so mice no longer avoided the allergen.Medzhitov said that the findings illustrate how the immune system evolved to help animals avoid dangerous ecological niches. Understanding how the immune system memorises potential dangers, he added, could one day help suppress excessive reactions to many allergens and other pathogens.