Links between the immune system and the brain grow ever stronger.
The study of human social behavior is a dense and difficult endeavor.
It calls for expertise in a range of disciplines, from psychology to sociology and neuroscience to ethnology.
Following the research covered below, that list of specialties may soon include immunology.
Until relatively recently, the brain and immune system were considered to work in isolation from each other. This is now known not to be the case.
A team of researchers from the University of Virginia (UVA) School of Medicine has gone one step further, showing that the immune system not only affects social behavior, it might even exert control over it.
The brain and the immune system
Although certain observations seemed to point to a link between the immune system and neurological functioning - psychological stress slows wound healing, for instance - it was not until the 1970s that the picture became clearer. Robert Ader demonstrated that an immune response could be conditioned in rats, proving once and for all that there were intimate ties between the two systems.
Since those early days, a new discipline, sometimes referred to as psychoneuroimmunology, has sprung up to study this fascinating field.
An investigation carried out last year by Jonathan Kipnis, Ph.D., chairman of UVA's Department of Neuroscience, uncovered further connections between the brain and immune system. Specifically, they found links between the vessels of the meninges (layers of tissue that coat the central nervous system) and the lymphatic system (an immune highway).
This discovery reversed the common belief that the brain was "immune privileged" and lacked direct communication between the two systems.
Kipnis's latest endeavor sheds even more light on brain-immune interaction. The team found that an immune molecule - interferon gamma - might play an important role in social behavior.
The relationship between people and pathogens
Interferon gamma is normally released in response to a pathogen attack, whether a virus, bacteria, or parasite. A number of animals, including zebrafish, flies, rats, and mice also activate interferon gamma when they are being social.
For the current study, the researchers blocked this molecule from taking effect in mice brains. This genetic modification caused hyperactivity in the brains of the animals. They became significantly less social. Once the molecule was reintroduced, brain connectivity returned to normal levels, and social behavior resumed.
The findings hint at a wider role for the immune system in social interaction.
"It's extremely critical for an organism to be social for the survival of the species. It's important for foraging, sexual reproduction, gathering, hunting. So the hypothesis is that when organisms come together, you have a higher propensity to spread infection. So you need to be social, but [in doing so] you have a higher chance of spreading pathogens.
The idea 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."
Lead author Anthony J. Filiano, Ph.D., Hartwell postdoctoral fellow
According to the researchers, an immune system that is not working correctly could be involved in social problems related to neurological and psychiatric disorders. This research is but the first step along what promises to be a bountiful path of discovery. The implications for autism and other conditions could be huge, but it is too early to make predictions.
The future of the brain-immune complex
Both neuroscience and immunology still hold many secrets, they are almost unimaginably complex; therefore, any interaction between the two is bound to take time to unpick.
No single molecule is likely to be responsible for a condition with a social dysfunction aspect, but the discovery that the immune system and, therefore, germs have some influence over social interaction opens new and exciting routes toward innovative interventions.
Kipnis told Medical News Today that he plans to follow this research up by investigating other immune molecules' effects on the brain and, eventually, how they impact human interaction.
MNT also asked how he expects this new area of research to pan out:
"I think the neuroscientists are more and more understanding that there is more to brain function than just neurons. [...] immune cells could be seen as the cooling system of your car. Without an engine, the car will not work, but, without the cooling system, the engine will get overheated and won't function for long either. "
Exactly how much influence the immune system has on brain development and function is yet to be uncovered. But, as Kipnis says, it is not just the clinical implications that are intriguing, also "the philosophical aspects of this work are very interesting."