Laboratory mice may just have overturned a decades-old theory of the brain being immune-isolated. A new study has found clinching evidence suggesting the immune system defines social behavior.
Through the study, University of Virginia's Anthony J. Filiano and team demonstrated how blocking an immune molecule called interferon gamma (G) in mice caused the animals' brain to turn hyperactive and rendered them less social. Interferon G is associated with immunity, released by lymphatic T-cells in response to pathogens. This finding adds to an earlier find by the team showing a physical connection between the meningeal vessels of the brain and the lymphatic system responsible for immunity in humans. Restoring the molecule also restored normal brain function and social behavior.
"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 pathology. And now, not only are we showing that they are closely interacting, but some of our behavior traits might have evolved because of our immune response to pathogens," explained Jonathan Kipnis, chair of UVA's Department of Neuroscience.
To explain their findings, researchers suggest an evolutionary connection between social interactions and immunity. Survival of humans was dependent on social interactions within the species, which in turn could have helped evolve our immunities as social interactions are opportunities for bacterial and viral spread. Through the mice study published in Nature, it is being suggested evolution shaped our immune response that directs social behavior.
So what does all this imply? For starters, it could help better understand the causes of autism spectrum disorders which are attributed to a multitude of causes, most being unknown.
"Using this approach we predicted a role for interferon gamma, an important cytokine secreted by T lymphocytes, in promoting social brain functions," Vladimir Litvak, a researcher at University of Massachusetts who collaborated with UVA scientists. "Our findings contribute to a deeper understanding of social dysfunction in neurological disorders, such as autism and schizophrenia, and may open new avenues for therapeutic approaches."