Multiple sclerosis (MS) is a complex, progressive disorder that severely affects the nervous system, rendering sufferers unable to control their muscles and faced with various cognitive problems, like difficulties understanding language. It is caused by the rogue behavior of a specific type of white blood cell, but a new study published in Science Translational Medicine reveals that a second hidden antagonist may be partly to blame.

Currently incurable, the disorder is caused by the destruction of the nervous system by the immune system by rogue white blood cells called T cells. At the onset of MS, they are able to enter the brain through the blood-brain barrier, a lattice-like network separating the circulating blood from the central nervous system’s “extracellular fluid,” which helps move water, salts and minerals through the body. The T cells encounter the fat-based insulation (myelin sheaths) around the nerve cells in the brain and spinal cord and automatically attack it, recognizing it as a foreign invader.

As these nerve cells (neurons) are exposed by the attack, they become increasingly damaged over time. This results in an inflammatory process throughout the nervous system, disrupting its ability to operate normally. The reason why the T cells begin attacking the myelin sheaths is unclear.

This new study – led by researchers at the Montreal Neurological Institute, the Hospital of McGill University and the McGill University Health Centre, Canada – notes that emerging studies have found a second set of cellular perpetrators, B cells, are actually significant contributors to the disorder. This new research has shed some more light on the behavior of B cells, revealing the specific types of B cell that are involved in MS, each of which displays its own unique behavior.

Although some B cells have the ability to limit inflammation, others are able to induce inflammation similar to the way T cells do, and by looking at MS patients and comparing them to healthy subjects, the specific pro-inflammation B cells were identified. These “bad” B cells were found to be more prone to activation in MS patients.

It was already known that removing large quantities of B cells from the body using a technique called B cell depletion therapy (BCDT) dramatically reduces the symptoms of the most common type of MS, but this new research indicates precisely why this is. Now that the malevolent B cells can be differentiated from the benevolent B cells, future BCDT will aim to only target the rogue white blood cells and leave the “good” ones intact in the body.

White blood cells, including “good” B cells, are the “police force” of the immune system, hunting down and destroying dangerous invading microbes. So, BCDT that leaves the normal B cells in the body will allow the patient’s immune system to remain in better shape than the current, indiscriminate B cell removal method does.