The body's immune system is designed to make us hide away when we get sick. But modern life could be sending this recovery response off track

Brain under siege

MIKE had struggled with depression his whole life, but one day in 1995 it all got too much. “I completely fell apart,” he says. “I backed out of life.”

Mike tried to kill himself with an overdose of prescription painkillers. Medics saved him, but the next 15 years of treatment brought little respite. He cycled through dozens of types of antidepressants, with side effects including sickness, insomnia and anxiety. Nothing worked.

Then, in 2010, Mike received a call from his doctor, offering him the chance to take part in a clinical trial. Rather than targeting brain chemistry, as most standard antidepressants do, this was a trial of a drug normally reserved for Crohn’s disease, an inflammatory bowel condition where the body’s immune system attacks the gut. Desperate for a break, he signed up. And it worked. About a week after the first treatment, the fog of depression cleared. “I just sort of woke up,” Mike says.

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This trial is one of a growing number of studies probing the idea that the inflammatory response, which normally helps us when we get sick, might occasionally wreak havoc in the brain. It has been implicated in a number of disorders – from depression to schizophrenia and Alzheimer’s disease.

That such a well-understood physical process might lie behind these brain disorders is a cause for optimism – turn off the inflammatory signals in the body, and you might be able to modify or even banish the symptoms in the …