Researchers at the University of Zurich, the University Hospital Zurich, and the Karolinska Institute in Sweden discovered a key aspect in the pathogenesis of MS. They were able to show for the first time that certain B cells – the cells of the immune system that produce antibodies – activate the specific T cells that cause inflammation in the brain and nerve cell lesions. The researchers said their findings not only explain how new MS drugs take effect, but also pave the way for novel approaches in basic research and therapy for MS.

Until recently, MS research had mainly focused on T cells, or T helper cells. They are the immune system's "guardians," which for example sound the alarm if the organism is infected with a virus or bacteria. The cells' ability to distinguish between the body's own and foreign structures becomes disturbed in about one in a 1,000 people. The effect of this is that the misguided T cells start to attack the body's own nerve tissue – the onset of MS. However, the T cells aren't the sole cause of this.

The researchers established the role of B cells by using an experimental in-vitro system that allowed blood samples to be analyzed. The blood of people with MS revealed increased levels of activation and cellular division among those T cells attacking the body's myelin sheaths that surround nerve cells. This was caused by B cells interacting with the T cells. When the B cells were eliminated, the researchers found that it very effectively inhibited the proliferation of T cells.

Researchers also discovered that the activated T cells in the blood notably included those that also occur in the brain in MS patients during flare-ups of the disease. It is suspected that they cause the inflammation. Further studies showed that these T cells recognize the structures of a protein that is produced by the B cells as well as nerve cells in the brain. After being activated in the peripheral blood, the T cells migrate to the brain, where they destroy nerve tissue. 

The findings were published in the journal Cell.