Humans depend on six senses to help them navigate the world – sight, hearing, smell, touch, taste and our sense of position and movement. Now, a scientist at the University of Virginia is suggesting we may have a seventh sense – a theory that has landed him on the cover of Scientific American and Nature magazine.
His discovery could have important implications for the treatment of diseases, including Alzheimer’s and autism.
Doctors and medical scientists have long believed that our nervous system and brain were completely separate from our immune system, but Dr. Jonathan Kipnis, chairman of the Department of Neuroscience at UVA, is compiling evidence to the contrary. He’s shown, for example, that mice don’t learn well without a healthy immune system.
“If we remove a particular type of immune cell mice cannot learn a maze task,” he says.
Mice also show signs of stress when exposed to the smell of cat urine. “And then if you test them after about a week, roughly 10-15% of mice will actually show this long-term stress response which actually was developed as a model for PTSD, post traumatic stress disorder, and what we've noticed if you take mice without without normally functioning immune system, instead of 10-15%, you will have 70-80% of mice will develop PTSD.”
Kipnis says immune cells flood the brain and spinal cord in the event of injury – and while they can’t prevent damage, they do promote healing. All of this begs the question: how is the brain connected to the immune system? Back in the 17th century, a doctor in Austria created a wax model showing vessels running through the outer layer of the brain. He thought they were not blood but lymph vessels carrying waste, but no one believed him, but more than 200 years later the team led by Kipnis re-discovered what is in fact part of the lymphatic system.
“It takes all the garbage that the tissue produces, and takes it through the lymph nodes, and the lymph nodes are, if you wish, the command center of the immune system. Two different sub-types of flu strain and your immune system will know exactly which one is which. The precision is exceptional, and so what I suggest is could it be that the immune system is there to sense the micro-organisms and then inform the brain about them? ”
Like other biological functions, the lymphatic system can begin breaking down as we age – but in mice, Kipnis and his team were able to improve function using a specific growth factor.
“Actually we’re shaving the skull, putting it in a gel. Maybe in the future we were joking that it could be a shampoo, so we’re applying this gel with this growth factor for about a month. It interacts with lymphatic epithelial cells, and makes them grow so the vessel becomes rejuvenated. It becomes wider, and it drains the fluid better.”
And that, he adds, translated into a better ability to learn and remember. “When we tested those aged mice, which usually perform very poorly on cognitive tasks, after treatment with this growth factor they actually were much, much better than their controls.”
Because the immune system monitors our environment and -- like the eyes, ears or nose -- helps the brain to send the right reaction signals, Kipnis argues it could be our seventh sense.
This science is relatively young – a long way from having practical implications for humans, but Kipnis is excited. It isn’t easy to get certain medications into the brain because of something called the blood brain barrier, but we are able to bolster the immune system and to stimulate lymphatic function, and by doing so we might find new ways to approach Alzheimer’s and other destructive neurological disease.
Editor's Note: The University of Virginia is a financial supporter of Radio IQ.