In diseases such as multiple sclerosis, cells of the immune system infiltrate the brain tissue, where they cause immense damage. For many years, it was an enigma as to how these cells can escape from the bloodstream. This is no trivial feat, given that specialized blood vessels act as a barrier between the nervous system and the bloodstream. Until now, tissue sections provided the sole evidence that the immune cells really do manage to reach the nerve cells. Now, a team of scientists from the Max Planck Institute of Neurobiology, the University Medical Center Göttingen, and other institutes, has witnessed the movements of these cells "live" under the microscope for the very first time. In the process, they discovered several new behavioural traits of the immune cells. The consolidated findings mark a significant step forward in our understanding of this complex disease. (Nature,14 October 2009)

The brain and the spinal cord monitor and control the functions of all body parts and co-ordinate the whole organism's movements, senses and behaviour. Adequate protection of the brain and spinal cord are therefore of the utmost importance. Physical influences and injuries are warded off by the cranial bone and the vertebral column. Dangers lurking within the body, such as viruses circulating in the bloodstream, are kept at bay by highly specialized blood vessels. The vessels' walls form a barrier that cannot be penetrated by the cells or various other small particles, thus serving to protect the delicate nerve cells.

There are, however, exceptions to the rule. In diseases such as multiple sclerosis (MS), aggressive cells in the immune system manage to break through the blood vessels' barrier. Having invaded the brain tissue, these cells wreak havoc by triggering off inflammatory reactions and attacking nerve cells. In Germany alone, the resulting adverse effects afflict over 120,000 MS-patients.

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