* Salt may increase production of inflammatory cells in some
* Researcher to study if salt reduction helps MS patients
By Julie Steenhuysen
CHICAGO, March 6 Increased salt consumption may
be a key culprit behind rising rates of autoimmune diseases such
as multiple sclerosis, researchers reported on Wednesday in a
trio of papers looking at the role of a specific class of cells
linked with inflammation.
Reporting in the journal Nature, the researchers said
high-salt diets increased levels of a type of immune cell linked
with autoimmune disease. And mice genetically engineered to
develop multiple sclerosis (MS) got much worse when they ate
what amounted to a high-salt Western diet compared with mice who
had more moderate salt intake.
The findings suggest that salt may play a previously unknown
role in triggering autoimmune diseases such as MS or type 1
diabetes in individuals who are already genetically predisposed.
"It's not bad genes. It's not bad environment. It's a bad
interaction between genes and the environment," said Dr. David
Hafler, a professor of immunobiology at Yale University in New
Haven, Connecticut, and senior author of one of the three
High salt intake is already a known culprit in increasing
the risk of heart disease and hypertension. The new study now
implicates high-salt diets in increasing rates of autoimmune
disease. "It can't be just salt. We know vitamin D probably
plays a small component. We know smoking is a risk factor. This
now suggests that salt is also a risk factor," Hafler said.
"How much? We don't know," he added.
Hafler became interested in studying the link between salt
and autoimmunity through studies of the gut microbiome - a
census of gut microbes and cell function of 100 healthy
The team noticed that when people in the study visited fast
food restaurants more than once a week, they saw a marked
increase in levels of destructive inflammatory cells, which the
immune system produces to respond to injury or foreign invaders,
but which attack healthy tissues in autoimmune diseases.
He shared these findings with colleagues at Harvard Medical
School and the Broad Institute of Harvard and the Massachusetts
Institute of Technology and others who were working out what
factors induce the activity of a type of autoimmune cell known
as a T helper 17 or a Th17 cell.
Th17 cells can promote inflammation that is important for
defending against pathogens, but they have also been linked to
diseases like multiple sclerosis, psoriasis, rheumatoid
arthritis, and ankylosing spondylitis. Treatment options for
some of these diseases, such as psoriasis, include manipulating
T cell function.
"The question we wanted to pursue was: How does this highly
pathogenic, pro-inflammatory T cell develop?" said Vijay Kuchroo
of the Harvard-affiliated Brigham and Women's Hospital and a
member of the Broad Institute.
"Once we have a more nuanced understanding of the
development of the pathogenic Th17 cells, we may be able to
pursue ways to regulate them or their function."
Hafler said Kuchroo's team worked on tracing how these
immune cells were wired, and what triggered their development.
They identified a specific gene known as SGK1 that plays an
important role in the cells' development. This gene had not been
seen in T cells before, but it has been known to play a role in
absorbing salt in the gut and kidneys.
"We put the two together and went after this," Hafler said.
Researchers at Harvard and Yale and colleagues in Germany
led by Dominik Mueller looked to see whether a high-salt diet
could induce the destructive immune system response that is the
hallmark of autoimmunity.
They found that adding salt to the diet of mice induced the
production of Th17 cells and that mice genetically engineered to
develop a form of MS had more severe disease than mice fed a
normal mouse diet.
Hafler says the findings now need to be studied in people.
He has already gotten permission to test the effects of lowering
the salt intake in the diets of individuals with multiple
sclerosis to see if their symptoms improve.
It likely be years before this link is confirmed, but Hafler
says for patients already at risk of autoimmune disease,
reducing dietary salt may be a good idea.
"If I had MS, I would think very much about not eating
processed foods and really cutting down my salt intake," he
(Reporting by Julie Steenhuysen; Editing by Cynthia Osterman)