In a startling discovery that raises fundamental questions about human behavior, researchers at the University of Virginia School of Medicine have determined that the immune system directly affects – and even controls – creatures’ social behavior, such as their desire to interact with others.
So could immune system problems contribute to social anxiety? The answer appears to be yes, and that finding could have significant implications for neurological diseases such as autism-spectrum disorders and schizophrenia.
Prior to this study, 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. The findings now show that not only are they closely interacting, but some behavior traits might have evolved due to the body’s immune response to pathogens. Think of it this way: Our bodies may just be multicellular battlefields for two ancient forces: pathogens and the immune system. Part of our personality may actually be dictated by the immune system.
Just last year, it was discovered that meningeal vessels directly link the brain with the lymphatic system. That overturned decades of textbook teaching that the brain was “immune privileged,” lacking a direct connection to the immune system. This discovery opened the door for entirely new ways of thinking about how the brain and the immune system interact.
Is it an evolutional thing?
The follow-up finding is equally illuminating, shedding light on both the workings of the brain and on evolution itself. The relationship between people and pathogens could have directly affected the development of our social behavior, 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. Social behavior is, of course, in the interest of pathogens, as it allows them to spread.
Researchers have shown that a specific immune molecule, interferon gamma, seems to be critical for social behavior and that a variety of creatures, such as flies, zebrafish, mice and rats, activate interferon gamma responses when they are social. Normally, this molecule is produced by the immune system in response to bacteria, viruses or parasites. Blocking the molecule in mice using genetic modification made regions of the brain hyperactive, causing the mice to become less social. Restoring the molecule restored the brain connectivity and behavior to normal. In their findings, researches noted that the immune molecule plays a “profound role in maintaining proper social function.”
For survival of the species, it’s critical for an organism to be social (gathering, hunting, sexual reproduction etc). When organisms come together, you have a higher propensity to spread infection. So, organisms need to be social to survive, but in doing so there is a much higher chance of spreading pathogens. The hypothesis is that interferon gamma, in evolution, has been used as a more efficient way to both boost social behavior while boosting an anti-pathogen response.
Understanding the implications
The researchers note that a malfunctioning immune system may be responsible for “social deficits in numerous neurological and psychiatric disorders.” But exactly what this might mean for autism, social anxiety, and other specific conditions requires further investigation. It is unlikely that any one molecule will be responsible for disease or the key to a cure. The researchers believe that the causes are likely to be much more complex. But the discovery that the immune system – and possibly germs, by extension – can control our social interactions raises many exciting avenues for scientists to explore, both in terms of battling neurological disorders, and understanding human behavior.