High Immune Cell Counts in Blood May Be Linked to MS, Study Finds

Higher numbers of immune cells circulating in the bloodstream may mean a greater likelihood of developing multiple sclerosis (MS), according to a study based on a large pool of genetic data in people of European ancestry.

One particular type of immune cell, called natural killer (NK) cells, was linked to a 24% increase in the chance of having MS. Understanding the role played by NK cells in this disease may raise new possibilities for potential therapies, the researchers noted.

The study, “The effect of peripheral immune cell counts on the risk of multiple sclerosis: a Mendelian randomization study,” was published in Frontiers in Immunology.

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There are many possible causes of MS, including genetic factors. About 1 in 5 patients have a family history of the disease, and many of the genes linked to MS give instructions for making proteins needed for the immune system.

Various approved treatments for MS are designed to modulate the inflammatory response that causes damage to the nervous system.

“Early treatment with drugs that reshape the immune environment can indeed limit the rate of evolving to the secondary progressive stage,” the researchers wrote.

To further support the view that MS is an immune-mediated disease, a team in China set out to determine whether genetically predicted immune cell counts may have a causal effect on MS. To do this, variations in genes of known function were used as proxies of immune cell counts.

The team set out using data from the international Blood Cell Consortium, which includes over 560,000 people of European descent, to determine how genetic variants affect immune cell counts in the bloodstream. Information on certain subtypes of immune cells came from data covering 3,757 people in Sardinia, an Italian island.

Then, data from the International Multiple Sclerosis Genetics Consortium (IMSGC) — which includes 47,429 patients with MS and 68,374 healthy controls of European ancestry, the study noted — was used to examine the causal effect of immune cell counts on MS.

Higher numbers of leukocytes (white blood cells) increased the likelihood of having MS by 24%, results showed. Among the five types of white blood cells examined, lymphocytes — which include T-cells, B-cells, and other cells known to contribute to MS damage — increased the chances of MS by 17%.

“This study provides evidence that higher circulating leucocyte and lymphocyte counts increase the risk of MS,” the researchers wrote.

Due to the small sample size in the Sardinian dataset, the team was only able to examine the effect of genetic variants on six lymphocyte subtypes. An effect on MS likelihood, in other words, could only be determined for those immune cells. Results showed that higher genetically predicted numbers of NK T-cells increased the likelihood of having MS by 24%.

NK T-cells serve as sentinels of the immune system and provide a first line of defense from an infection. They also send off alarm signals to ask for the help, bringing other immune cells to sites of inflammation occurring in response to infection. Their role in MS is still controversial.

While the findings suggest a causal link between NK T-cells and MS, “further genetic profiling using [a] diverse European population is recommended,” the researchers wrote.

Nevertheless, the link “underscores the relevance of exploring the functional roles of NKT cells in MS,” they added.