This could be a very significant development in medical research: Multiple sclerosis is an autoimmune disease affecting both adults and children. It's driven by 'helper' T cells, white blood cells that mount an inflammatory attack on the brain and spinal cord, degrading the protective myelin sheath that covers nerve fibers. But there are many different kinds of T helper cells, and up until now, no one knew which ones were the bad actors. Researchers at Boston Children's Hospital have now pinpointed the specific helper T cells that cause MS, as well as a protein on their surface that marks them. As reported this week in PNAS, an antibody targeting this protein, CXCR6, both prevented and reversed MS in a mouse model.