BBC health reporter James Gallagher explores the increasing body of evidence that a dysfunctional immune system is responsible for the depression or psychotic illness experienced by hundreds of thousands, perhaps millions, of people in the UK.
He talks to the psychiatrists investigating this new understanding of mental illness and to people who may benefit from treatments aimed at the immune systems rather than their brain cells.
Belinda Lennox takes James to the neuroimmunology lab in Oxford where antibodes are tested in patients' blood, and where treatments can be offered.
Listen to The Inflamed Mind here.
Dr Belinda Lennox begins at 11.30