Videos show T cells breaching the central nervous system's defences.A T cell (green) is seen moving with the flow of blood before crawling against it and exiting the blood vessel.Ingo Bartholomaeus et al, Nature 2009 Despite being surrounded by a supposedly unbreachable defensive line, the body's central nervous system can still be attacked by autoimmune diseases such as multiple sclerosis.Now, researchers led by Alexander Flügel, director of the Institute for Multiple Sclerosis Research at the University Medical Centre in Göttingen, Germany, have watched in real time as T cells — blood cells linked to the immune response — penetrate the...