Kevin Tracey, a neurosurgeon based in New York, is a man haunted by personal events – a man with a mission. “My mother died from a brain tumour when I was five years old. It was very sudden and unexpected,” he says. “And I learned from that experience that the brain – nerves – are responsible for health.” This drove his decision to become a brain surgeon. Then, during his hospital training, he was looking after a patient with serious burns who suddenly suffered severe inflammation. “She was an 11-month-old baby girl called Janice who died in my arms.” These traumatic moments made him a neurosurgeon who thinks a lot about inflammation. He believes it was this perspective that enabled him to interpret the results of an accidental experiment in a new way.
In the late 1990s, Tracey was experimenting with a rat’s brain. “We’d injected an anti-inflammatory drug into the brain because we were studying the beneficial effect of blocking inflammation during a stroke,” he recalls. “We were surprised to find that when the drug was present in the brain, it also blocked inflammation in the spleen and in other organs in the rest of the body. Yet the amount of drug we’d injected was far too small to have got into the bloodstream and travelled to the rest of the body.”
After months puzzling over this, he finally hit upon the idea that the brain might be using the nervous system – specifically the vagus nerve – to tell the spleen to switch off inflammation everywhere.
It was an extraordinary idea – if Tracey was right, inflammation in body tissues was being directly regulated by the brain. Communication between the immune system’s specialist cells in our organs and bloodstream and the electrical connections of the nervous system had been considered impossible. Now Tracey was apparently discovering that the two systems were intricately linked.