a, Bacteria of the genus Lactobacillus, such as L. murinus, convert the dietary amino acid tryptophan into compounds called indoles in the lumen region of the gut. Wilck et al.2 have demonstrated in mice that one of these indoles prevents differentiation of immune cells called T lymphocytes into TH17 cells in the gut mucosa. b, The authors showed that feeding mice a high-salt diet causes a decrease in the levels of L. murinus in the gut. This diet and decrease in L. murinus was associated with an increase in the number and activation of TH17 cells. These cells produce a pro-inflammatory molecule called interleukin-17 (IL-17), which is thought to promote high blood pressure (hypertension) and accompanying inflammation in artery walls, and exacerbate an autoimmune disease in mice dubbed actively induced experimental autoimmune encephalomyelitis (EAE).