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Modern scientific understanding has considered multiple sclerosis (MS) to be a disease controlled by the T cell, a type of white blood cell. Research has shown that in MS, T cells inappropriately attack myelin, the protective layer of fat covering nerves in the central nervous system, exposing them to damage.

Emerging studies have also discovered that B cells, another type of white blood cells that had previously been overlooked in MS, are significant contributors to the disease. Recent clinical trials revealed that B cell depletion Therapy (BCDT) in people with relapsing-remitting MS led to dramatic decreases in new disease activity. But how B cells contribute to the disease and the molecular mechanisms involved in the benefit of BCDT has not been fully elucidated.

The study by Dr. Amit Bar-Or at the Montreal Neurological Institute and Hospital and colleagues and published in the October issue of Science Translational Medicine, provides groundbreaking insight into the role听of B cells and their complex interaction with other immune cells in the context of MS.

鈥淲e鈥檝e recently discovered that different types of human B cells exist. Some B cells have been shown to promote inflammation, while others are actually able to limit inflammation.听 Our study has implicated a subset of B cells, the GM-CSF producing B cells, as a key contributor in the pro-inflammatory immune cells responses at play in MS,鈥� explained Dr. Amit Bar-Or, Director of the Experimental Therapeutics Program and Scientific Director of the Clinical Research Unit, at the Montreal Neurological Institute and senior author of the study.

The study first examined samples of MS patients comparing them to healthy subjects. Researchers discovered that GM-CSF producing B cells were more frequent and more prone to activation in MS patients. This subset of B cells was able to activate pro-inflammatory responses of myeloid cells of the immune system Confirming these results in patients, the researchers found that after B cell depletion Therapy (BCDT), the myeloid cells became much less pro-inflammatory, suggesting that BCDT may work in part by decreasing the number of GM-CSF鈥損roducing B cells and in turn limiting both myeloid cell and T cell contribution to new disease activity.

鈥淭he study is significant in discovering a new way by which B cells can contribute to abnormal immune responses in MS which reinforces the rationale for the use of B cell depletion therapy. Furthermore, better identifying the particular subset of B cells responsible for new disease activity, we can look forward to more selectively targeting the 鈥渂ad鈥� B cells while leaving 鈥済ood鈥� B cells intact. This is important because B cells normally play key roles in our immune system, so more selective therapies offer the prospect of decreasing the risk of impairing the patients鈥� immune system in the long run.鈥�

An estimated 100,000 Canadians live with multiple sclerosis; there is currently no cure for the disease. This study shows promise for the development of the next generation of targeted treatments that could one day听provide a cure for this debilitating disease.

, conducted by Rui Li a PhD student in the lab of Dr. Amit Bar-Or at the Montreal Neurological Institute was carried out as part of the Canadian B cells in MS Team, involving Dr. Jen Gommerman at the University of Toronto and Dr. Alexandre Prat at the CHUM, and was supported by a collaborative team grant from the Multiple Sclerosis Society of Canada and the Multiple Sclerosis Scientific Research Foundation.

About multiple sclerosis, the MS Society of Canada and the Multiple Sclerosis Scientific Research Foundation
Canada has the highest rate of multiple sclerosis in the world. MS is a chronic, often disabling disease of the central nervous system comprising the brain, spinal cord and optic nerve. It is one of the most common neurological diseases affecting young adults in Canada. Most people with MS are diagnosed between the ages of 15 and 40, and the unpredictable effects of MS last for the rest of their lives. The MS Society provides services to people with MS and their families and funds research to find the cause and cure for this disease. The Multiple Sclerosis Scientific Research Foundation funds large, innovative, multi-centre collaborative studies that will lead to major advances in the field of MS. A unique Canadian resource, the Foundation鈥檚 main funding source is the MS Society of Canada. Please visit or call 1-800-268-7582 to make a donation or for more information.

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