Multiple sclerosis is an autoimmune disease: white blood cells attack the myelin sheath that protects nerve fibers in the spinal cord and brain  Medical science now has a drug that can be used to successfully treat multiple sclerosis, but the path that led medical researchers to this drug was hardly straightforward  Initially, some scientists believed attacks characteristic of multiple sclerosis might be triggered by chronic viral infections  So in 1984 they began testing gamma interferon, one of the body' s own antiviral weapons  To their horror, all the multiple sclerosis patients tested became dramatically worse
The false step proved to be instructive however
Gamma interferon stops white blood cells from producing myelin-destroying compounds.