High salt diet mediates the skin immune response

Salt in our diet has been linked with all sorts of nasty side effects such as hypertension and autoimmune disease.  Researchers from Germany, though, wondered how Na+ in our diet may be affecting the skin microbiome, especially during infection.   Our skin is an important physiological barrier between our body and our microbiome, and because it is partially covered in organisms whenever we get a cut we are at risk for infection.  Fortunately our skin is actually loaded with immune cells that help destroy any of these organisms that may cause harm, and they mitigate the risk for infection.  The German researchers recently discovered that Na+ in our skin may actually be critical for our body to properly fight these infections.  The results were published in Cell Metabolism.

The scientists first infected the skin of both humans and mice with a eukaryotic organism called Leishmania major, which is a common skin pathogen primarily found in Northern Africa and the Middle East.  When they observed the infections using MRI they discovered that the local Na+ concentration around the infection increased in concentration.  They then showed that after treatment of the infection with antibiotics the local Na+ decreased.  

The scientists speculated that the Na+ was perhaps helping to fight the infections, so they designed an experiment to test this hypothesis.  They fed two groups of mice a high salt diet or a no salt diet.  Then they infected the mice with L. major.  They showed that after infection the mice that had not eaten salt struggled to clear the infection, while those that had eaten the high salt diet cleared the infection quickly.  The researchers performed a series of experiments on these mice to learn the actual mechanisms by which salt mediated the immune response, and learned that the Na+ activates and promotes certain immune cells in the skin.

This study shows an unexpected benefit to salt in the diet.  Interestingly, the salt content of our skin increases with age.  While this process has been linked to hypertension, perhaps it also helps fight bed sore infections and other types of skin infections that primarily afflict the elderly.     

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