Yet another reason to watch out for salty food is that it may aggravate autoimmune conditions, including multiple sclerosis and psoriasis. A link has been identified in animals, but we don’t yet know whether it also holds for humans, says David Hafler of the Yale School of Medicine. If it does, it could provide new ways of controlling many autoimmune diseases. During the recent study, Hafler’s team added salt to white blood cells taken from mice and humans. The concentration was equivalent to what a high-salt diet would produce. For both species, the salt prompted the white blood cells to specialise into “interleukin 17-producing helper T cells”. These produce a molecule called interleukin 17A (IL-17A) that induces the destruction of pathogens. But IL-17A also aggravates inflammation in several autoimmune diseases. In human cells, excess salt caused the proportion producing IL-17A to soar from 2 to 40 per cent, and increased concentrations of IL-17A tenfold (Nature, DOI: 10.1038/nature11868). Similar results came from work carried out by a second team led by Vijay Kuchroo of the Brigham and Women’s Hospital in Boston (Nature, DOI: 10.1038/nature11868). Crucially, both labs showed they could prevent this response by silencing an enzyme that Kuchroo’s team discovered was a “salt sensor”. Blocking this sensor, called serum and glucocorticoid-regulated kinase 1, prevented salt from triggering the production of the helper T cells. Both teams gave food containing different levels of salt to mice bred to develop a form of multiple sclerosis. Mice fed a high-salt diet became completely immobile within a week, whereas those on low-salt diets lost only the ability to move their tails. Ari Waisman, who studies autoimmune diseases at the Johannes-Gutenberg University of Mainz in Germany, says that if the same mechanisms are at work in humans, psoriasis may be particularly affected because the condition recedes dramatically in people receiving antibodies that inhibit IL-17A. “Levels of IL-17A increase in MS patients, but the disease with a clear pathogenic role for IL-17A is psoriasis,” he says.
New Scientist, 6 March 2013 ;http://www.newscientist.com/ ;