(Credit: Getty Images)
Commonly associated with turkey, the amino acid tryptophan is found in lots of protein-rich foods, like dairy, nuts, and beans. Now scientists think it may play a key role in healthy guts.
Immune cells patrol the gut to make sure harmful microbes hidden in the food we eat don’t sneak into the body. Cells that are capable of triggering inflammation are balanced by cells that promote tolerance, protecting the body without damaging sensitive tissues.
“The more tryptophan the mice had in their diet, the more of these immune cells they had.”
But when the balance tilts too far in the wrong direction, inflammatory bowel disease can be the result.
Researchers have discovered that a kind of tolerance-promoting immune cell appears in mice that carry a specific bacterium in their guts. The bacterium needs tryptophan—one of the building blocks of proteins—to trigger the cells’ appearance.
“We established a link between one bacterial species—Lactobacillus reuteri—that is a normal part of the gut microbiome, and the development of a population of cells that promote tolerance,” says Marco Colonna, professor of pathology at Washington University in St. Louis and senior author of the study in the journal Science. “The more tryptophan the mice had in their diet, the more of these immune cells they had.”
If such findings hold true for people, it would suggest that the combination of L. reuteri and a tryptophan-rich diet may foster a more tolerant, less inflammatory gut environment, which could mean relief for the million or more Americans living with the abdominal pain and diarrhea of inflammatory bowel disease.
Postdoctoral researcher Luisa Cervantes-Barragan was studying a kind of immune cell that promotes tolerance when she discovered that one group of study mice had such cells, while a second group of study mice that were the same strain of mice but were housed far apart from the first group didn’t.
The mice were genetically identical but had been born and raised separately, indicating that an environmental factor influenced whether the immune cells developed.
Cervantes-Barragan suspected the difference had to do with the mice’s gut microbiomes—the community of bacteria, viruses, and fungi that normally live within the gastrointestinal tract.
The researchers sequenced DNA from the intestines of the two groups of mice and found six bacterial species present in the mice with the immune cells but absent from the mice without them.
They then turned to mice that had lived under sterile conditions since birth to identify which of the six species was involved in inducing the immune cells. Such mice lack a gut microbiome and don’t develop this kind of immune cell. When L. reuteri was introduced to the germ-free mice, the immune cells arose.