“It’s crazy, but maybe we are just multicellular battlefields for two ancient forces: pathogens and the immune system.”
Although we’d all like to think that we control our own personality and behaviors, new research suggests that we may not entirely be the captains of our ships. Instead, an unlikely candidate may be influencing our social behaviors: the immune system.
In an animal study, which has been published in Nature, researchers at the University of Virginia School of Medicine “have determined that the immune system directly affects – and even controls – creatures’ social behavior,” according to the press release.
By switching off one immune molecule, interferon-gamma, the researchers found that the way mice interacted with each other completely changed. The molecule is usually produced by the immune system in response to bacteria, viruses, or parasites.
By blocking the molecule, the mouse brains became overly connected, and the rodents became less willing to interact with each other. Once the molecule was switched back on, the brains were restored back to their normal state and regular social activities resumed.
"It’s crazy, but maybe we are just multicellular battlefields for two ancient forces: pathogens and the immune system," lead researcher Jonathan Kipnis, the chairman of UVA’s Department of Neuroscience, said in a press release. "Part of our personality may actually be dictated by the immune system."
Interestingly, up until last year, it was believed that the brain and the immune system didn’t even have the ability to interact with each other, due to the blood-brain barrier.
However, back in 2015, Kipnis and his team discovered that meningeal vessels link the brain with the lymphatic system, enabling them to directly interact with one another. This was the first finding of such an interaction that was previously thought to be impossible.
"The brain and the adaptive immune system were thought to be isolated from each other, and any immune activity in the brain was perceived as sign of a pathology," Kipnis explained in the press release. "And now, not only are we showing that they are closely interacting, but some of our behaviour traits might have evolved because of our immune response to pathogens."
Interestingly, this link between the brain and the immune system might offer new insights into conditions like depression, autism, and schizophrenia, which could somehow be triggered by the immune system. The researchers say that a malfunctioning immune system could play a role in “social deficits in numerous neurological and psychiatric disorders.”
Further, the researchers hypothesize that these findings may even implicate an evolutionary reason for the direct interaction between the brain and the immune system.
"The relationship between people and pathogens, the researchers suggest, could have directly affected the development of our social behaviour, allowing us to engage in the social interactions necessary for the survival of the species while developing ways for our immune systems to protect us from the diseases that accompany those interactions,” the press release states.
However, before jumping to any overdrawn conclusions, it’s important to note that further research has to confirm that these findings translate over to humans — the effect has only been demonstrated with mice, so far.
Still, "Immune molecules are actually defining how the brain is functioning. So, what is the overall impact of the immune system on our brain development and function?" said Kipnis. "I think the philosophical aspects of this work are very interesting, but it also has potentially very important clinical implications."
In the future, these findings may lead to new treatments for people with social disorders.