New Study Suggests Smoking May Play Larger Role in MS

Scientists have identified yet another way smoking is harmful to one’s health, and the latest discovery could have implications for the treatment of multiple sclerosis (MS) and a broad array of autoimmune conditions.

Scientists at the University of Copenhagen in Denmark, found that smokers have altered levels of certain immune cells, including lower frequencies of mucosal-associated invariant T (MAIT) than the general population. That’s significant, because MAIT is believed to play a role in autoimmune diseases. Although many researchers consider MS to be an autoimmune disease, according to the National Multiple Sclerosis Society, the classification is not universally accepted because scientists have yet to identify a specific antigen that could be linked to the immune reaction in patients with the disease.

In the new study, the Danish research team started out with a simple question: What impact, if any, does chronic smoking have on circulating immune cell subsets? To answer that, they examined the circulating immune cells of 100 healthy individuals (including smokers and nonsmokers), as well as 2 cohorts of patients with MS. One of the cohorts was made up of smokers; the other was made up of nonsmokers. In both the healthy and MS groups, the scientists found significant variances in the frequencies of certain cell types in smokers versus nonsmokers. They also found that T cells of smokers were not more proinflammatory or autoreactive in smokers versus nonsmokers.

While the research does not fully explore the link between smoking and the variances in cell frequencies, the researchers say they found enough interesting data to warrant significant additional study.

"We believe that our study represents an important contribution to the understanding of systemic immune cell alterations in smokers," said lead author Cecilie Ammitzbøll, MD, PhD (photo), of the Danish Multiple Sclerosis Center, in a press release. "From our findings we hope that focused research in specific cell populations might reveal pathogenic mechanisms contributing to the understanding of diseases associated with smoking."

Smoking is widely believed to speed up the progression from relapsing-remitting MS to secondary progressive MS. A 2005 study, for instance, found that smokers were more than 3 times more likely than nonsmokers to see their disease progress within 7 years.

Other research has suggested smoking might play a role in causing MS in some patients. A 2003 Norwegian study, for instance, showed smokers had a significantly higher chance of developing MS, compared to those who never smoked. However, like the Danish study, the Norwegian study also did not ascertain the specific mechanism by which smoking might affect MS risk.

"It is clear that smoking is detrimental to overall health and can predispose to many diseases," said John Wherry, PhD, deputy editor of the Journal of Leukocyte Biology, which published the Danish study. "These new studies shed light on how smoking can also influence the immune system, an effect that may have implications in autoimmunity and also in other settings such as cancer and chronic inflammatory diseases."

The study, titled, “Smoking reduces circulating CD26^hiCD161^hi MAIT cells in healthy individuals and patients with multiple sclerosis,” was published in the May issue of the Journal of Leukocyte Biology. It can be accessed online at this link.

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