Researchers from the University of Virginia’s Centre for Brain Immunology and Glia have made a remarkable discovery; the immune system has a direct and measurable impact on our social interactions.
For decades scientists have believed that the brain is “immune privileged”, meaning that there is no direct connection from the brain to the immune system. In 2015 Dr Kipnis of the UVA revealed that this was not the case. The lymphatic system is a vital part of the immune system which transports lymph, an infection-fighting
substance, through the body. Dr Kipnis found that there were lymphatic vessels lining the dural sinuses, which have a direct connection to the brain through connective tissues known as the meninges. This finding, published in Nature, goes against years of previous research, but a new study released this week helps to confirm the results.
Using genetic modification, Dr Filiano, alongside Dr Kipnis and his team, blocked the activity of an immune system molecule, interferon-γ. The molecule is normally
produced in response to bacteria, viruses or parasites but when the researchers blocked its production in mice, it had a profound effect. Fronto-cortical brain regions, which are associated with problem solving, spontaneity, memory, language, judgement, impulse control, social and sexual behavior, became hyperactive and as a result the mice became much less social. Conversely, when the gene was switched back on, both brain function and social behaviour was normalised.
The results suggest that interferon-γ has a direct effect on behaviour. Why might this be the case? Social behaviour is actually in the interest of pathogens because it allows them to spread across hosts and multiply. As explained by Dr Kipnis:
“It’s extremely critical for an organism to be social for the survival of the species [but] when organisms come together, you have a higher propensity to spread infection…the idea is that interferon gamma, in evolution, has been used as a more efficient way to both boost social behaviour while boosting an anti-pathogen response.”
A healthy immune system should increase production of interferon-γ and illicit positive social behaviours within the host. A malfunctioning immune system, however, could lead to dysfunctional behaviour and, according to the research paper, may even be responsible for “social deficits in numerous neurological and psychiatric disorders” such as autism and schizophrenia.
This research has huge implications for both healthy individuals and those who exhibit abnormal social behaviours. As expected, the researchers are very excited.
“It’s crazy, but maybe we are just multicellular battlefields for two ancient forces: pathogens and the immune system. Part of our personality may actually be dictated by the immune system.”
You can read the original journal article which was published in Nature.