Researchers from the University of Virginia School of Medicine and the University of Massachusetts Medical School have discovered that the immune system directly affects social behavior, even controlling the desire to interact with others.

In a study published in the journal Nature, Jonathan Kipnis and colleagues detailed their discovery, saying that problems with the immune system could affect the ability to socially interact normally. Their findings also have significant implications for understanding neurological diseases like schizophrenia and autism-spectrum disorders.

For decades, it has been thought that the brain and the immune system are isolated from each other. As such, any immune activity occurring in the brain region was seen as a sign of pathology. However, the researchers discovered in 2015 that meningeal vessels directly link the brain and the lymphatic system.

Kipnis and colleagues carried out further research to shed light on how the brain and evolution worked, suggesting that people and pathogens directly affect social behavior development, which paved the way for social interactions important to survival and immune system processes that offered protection from diseases that could be spread during those interactions.

"It's extremely critical for an organism to be social for the survival of the species ... but [in doing so], you have a higher chance of spreading pathogens," said Anthony J. Filiano, the study's lead author.

For the study, the researchers came up with a computational approach to examine the connection between the brain and the immune system and how that affects the health. They predicted that a certain immune system molecule secreted by T lymphocytes, called the interferon gamma, has a hand in promoting social functions in the brain.

True enough, interferon gamma appeared to be essential for social behavior, with various creatures like rats, mice, zebrafish and flies activating responses to the molecule while socializing.

Interferon gamma is normally produced by the immune system when responding to the threat of parasites, viruses or bacteria. When the molecule was blocked, the researchers observed that mice became less social. When it was restored, the mice's behavior returned to normal.

Given their findings, the researchers pointed out that it's possible for malfunctions in the immune system to be responsible for the social deficits seen in psychiatric and neurological disorders. However, further studies are needed to determine exactly how the current study will impact autism and other mental disorders.

The current study received funding support from the Hartwell Foundation and the National Institutes of Health.

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