Immune cells are present in the intestines to ensure that damaging microbes hidden in the meals that we consume do not sneak into the body. Cells that are in a position of triggering infection are balanced by cells that promote tolerance, protecting the body without bringing hazard to tissues. When the balance is disrupted, inflammatory bowel disease can ensue.

Now, researchers at Washington University School of Medicine in St. Louis have observed that a type of tolerance-creating immune cell is found in mice that carry a certain bacterium in their guts. Additionally, the bacterium wants tryptophan which is one of the building blocks of proteins, to bring about the cell's appearance.

According to Marco Colonna, MD, the Robert Rock Belliveau MD Professor of Pathology and the study’s senior author, 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. The more tryptophan the mice had in their diet, the more of these immune cells they had.�

If such findings can be applied to people, it would advocate that the blend of L.reuteri and a tryptophan-rich diet may foster a more tolerant, less inflammatory gut atmosphere, which could mean alleviation for millions of people living with abdominal pain and diarrhea that result from inflammatory bowel disease.

This study is published recently in the journal Science.

Postdoctoral researcher Luisa Cervantes-Barragan, PhD, was studying a variety of immune cells that promote tolerance when she had discovered that one group of study mice had such cells, at the same time when another group of study mice that is of identical strain but have been housed apart from the primary group didn’t have such cells.

The mice had been genetically equal but had been born and raised separately, indicating that an environmental factor influenced whether or not the immune cells developed.

She suspected the difference had to do with the mice’s gut microbiomes, which is the group of microorganisms that normally reside inside the gastrointestinal tract.

Cervantes-Barragan then collaborated with Chyi-track Hsieh, MD, PhD, the Alan A. and Edith L. Wolff exclusive Professor of medicine, to sequence DNA from the gut of the two groups of mice. They located that six bacterial species were present in the mice with the immune cells but were absent in the mice without them.

With the aid of Jeffrey I. Gordon, MD, the Dr. Robert J. Glaser exotic school Professor, the researchers studied mice that had lived on sterile environments since birth to determine which of the six species was involved in inducing the immune cells. Such mice lack a gut microbiome and do not create this sort of immune cell. When L. reuteri was given to the germ-free mice, the immune cells grew.

To appreciate how the bacteria affected the immune system, the researchers grew L. reuteri in liquid after which they transferred small amounts of the liquid without micro organisms to immature immune cells isolated from mice. The immune cells developed into the tolerance-promoting cells. When the active factor was purified from the liquid, it grew to become a byproduct of tryptophan metabolism referred to as indole-3-lactic acid.

Tryptophan, which was most of the time found in turkey, is ordinarily a part of the mouse and the human diet. Protein-rich foods contain considerable amounts, such as nuts, eggs, seeds, beans, poultry, yogurt, cheese, or even chocolate.

When the researchers doubled the amount of tryptophan within the mice’s feed, the number of such cells rose by about 50 percent. When the tryptophan levels were reduced to 50%, the number of cells also was reduced by half.

According to Cervantes-Barragan said, The development of these cells is probably something we want to encourage since these cells control inflammation on the inner surface of the intestines. Potentially, high levels of tryptophan in the presence of L. reuteri may induce expansion of this population.�