Granulomas are tissue nodules of immune cells that occur in diseases such as tuberculosis and sarcoidosis and can damage many organs. For the first time, a team of researchers has identified what causes them to form. It is the chronic activation of the metabolic sensor mTOR (mammalian Target Of Rapamycin) that is responsible for the formation of granulomas. The scientists also discovered that, in sarcoidosis (in which granulomas cause damage to the lungs), this mechanism leads to a course that is chronic and difficult to treat. Since mTOR inhibitors belong to a group of drugs already licensed for clinical use, these findings offer new and quickly testable treatment options.