According to scientists from the Max Planck Institute of Neurobiology in Martinsried, Germany, not harmful but beneficial bacteria of the natural intestinal flora, which every human being needs for digestion, trigger multiple sclerosis.

The likelihood of developing multiple sclerosis, a disease in which proteins on the surface of the myelin layer in the brain activate the immune system, is influenced by genes and environmental factors. The latter have an even greater impact on the disease’s development. Scientists have long suspected that it is caused by infectious agents.

The team around Gurumoorthy Krishnamoorthy discovered that genetically modified mice in the absence of exposure to any external influences, develop an inflammation in the brain similar to the human disease if they have normal bacterial intestinal flora. The microorganisms begin by activating the immune system’s T cells and, in a further step, the B immune cells.

The findings suggest that in humans with the corresponding genetic predisposition, the essentially beneficial intestinal flora could act as a trigger for the development of multiple sclerosis. Precisely which bacteria are involved remains unclear.

• Commensal microbiota and myelin autoantigen cooperate to trigger autoimmune demyelination,
  Kerstin Berer, Marsilius Mues, Michail Koutrolos, Zakeya Al Rasbi, Marina Boziki, Caroline Johner, Hartmut Wekerle, Gurumoorthy Krishnamoorthy,
  Nature 2011.
  DOI: doi:10.1038/nature10554