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A recent BWH study demonstrated a surprising connection between salt and autoimmunity, namely, that salt influences susceptibility to autoimmune diseases, including multiple sclerosis, rheumatoid arthritis and inflammatory bowel disease. In these types of diseases, the body does not recognize its own cells and tissues, and reacts against them.
The team, led by Vijay Kuchroo, DVM, PhD, co-director of the Infectious and Immunologic Diseases Center at BWH's Biomedical Research Institute and Samuel L. Wasserstrom Professor of Neurology in BWH's Department of Neurology, Kuchroo and his team found that they could induce more severe forms of autoimmune diseases, and at higher rates, in mice fed a high-salt diet than in those that were fed a normal diet.
Kuchroo notes, however, that the high-salt diet alone did not cause autoimmune diseases.
"It's not just salt, of course," said Kuchroo. "We have this genetic architecture-genes that have been tied to various forms of autoimmune diseases, and predispose a person to developing autoimmune diseases."
Leading up to the Salt Discovery
Arriving at the salt discovery involved first understanding the genetic makeup and growth of Th17 immune cells that have been found to induce autoimmune diseases. Researchers explored what the right activity levels of these cells should be when it comes to promoting a healthy immune system-too little activity leaves a person vulnerable to foreign invaders like fungal infections, but too much activity can harm the body and lead to autoimmune diseases.
They took 18 different snapshots of developing Th17 cells, to see what was happening inside them as they developed. Then, one-by-one, they silenced, or ‘switched off,' the genes responsible for making these cells, to see what would happen.
Researchers discovered that when one particular gene, called SGK1, was turned off in mice, Th17 cells were not produced. That specific gene had previously been found in gut and kidney cells, where it plays a role in absorbing salt.
Hence, when Kuchroo and his team further explored this observation by feeding mice a high-salt diet, the presence of the SGK1 gene in immune cells caused an increase in the amount of Th17 cells, leading to autoimmune disease.
Researchers note that there is still more to test and uncover, despite discovering that a salt-loving gene usually reserved to the gut and kidney also plays a role in immune cell activity.
"We suspect that environmental factors-infection, sunlight, smoking and vitamin D-may also play a role," said Kuchroo. "Salt could be one more thing on the list of predisposing environmental triggers that may promote the development of autoimmunity."
Researchers caution that it is still premature to claim that people should not consume salt for fear of increasing autoimmune disease risk. The connection needs to be further studied.
View a video interview with the researchers by the Broad Institute.