It works with mice, and it may work with people. Or not. Researchers at Washington University in St. Louis have found that a kind of tolerance-promoting immune cell appears in mice that carry a specific bacterium in their guts. But to trigger those immune cells, which appear to relieve inflammatory bowel disease, the bacterium need tryptophan – one of the building blocks of proteins – and one that is found in turkey and cheese. A Washington University news release reports that the researchers established a link between Lactobacillus reuteri – a normal part of the gut microbiome, and the development of a population of cells that promote tolerance. The more tryptophan the mice had in their diet, the more of these immune cells they had. When the researchers doubled the amount of tryptophan in the mice’s feed, the number of such cells rose by about 50 percent. When tryptophan levels were halved, the number of cells dropped by half. Tryptophan — commonly associated with turkey — is a normal part of the mouse and the human diet. Protein-rich foods contain appreciable amounts: nuts, eggs, seeds, beans, poultry, yogurt, cheese, even chocolate.