• The probiotic Lactobacillus reuteri appears to work well with the amino-acid tryptophan in promoting tolerance in immune cells of the gut – a way of reducing gut inflammation.
• Tryptophan is a critical amino-acid for building proteins.

The immune cells rove around the gut gobbling up microbes which are lurking in food so they don’t enter our bodies and cause trouble. Likewise, cells which trigger inflammation are aided and balanced by those cells promoting tolerance that protect tissues without damaging sensitive cells. If inflammation occurs then inflammatory bowel disease (IBS) takes over.

A piece of research in mice on protein feeding and IBS has been released by the Washington University School of Medicine in St. Louis. A kind of tolerance-promoting immune cell appears in mice that carry a certain defined bacterium in their guts. This particular bacterium requires tryptophan which is one of the building blocks of proteins, and helps trigger these immune cells to appear.

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.

The Role Of The Gut Flora & Fauna

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.

For the study, the team looked at  two groups of mice. One group of study mice had a kind of immune cell that promotes tolerance, whilst the other group were the same strain of mice but were housed far from the first group and they did not have such immune cells. The mice were genetically identical but had been born and raised separately, indicating that an environmental factor influenced whether the immune cells developed or not.

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 those 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.

To understand how the bacteria affected the immune system, researchers grew L. reuteri in liquid and then transferred small amounts of the liquid, without bacteria, to immature immune cells isolated from mice. The immune cells developed into the tolerance-promoting cells. When the active component was purified from the liquid, it turned out to be a byproduct of tryptophan metabolism known as indole-3-lactic acid.

Marco Colonna, MD. who is the Robert Rock Belliveau MD Professor of Pathology and the study’s senior author has quoted:-

“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.”

Tryptophan is a normal part of the human as well as mouse (murine) diet. Protein-rich foods—nuts, eggs, seeds, beans, poultry, yogurt, cheese, and treats like chocolate all contain appreciable amounts of this particular amino-acid. Doubling the amount of tryptophan in the mice’s feed caused the number of immune cells rose by about 50 percent. When tryptophan levels were halved, the number of cells dropped by half.

People have the same tolerance-promoting cells as mice, and most of us shelter L. reuteri in our gastrointestinal tracts. It is not known whether tryptophan byproducts from L. reuteri induce the cells to develop in people as they do in mice, but defects in genes related to tryptophan have been found in people with inflammatory bowel disease.

Cervantes-Barragan says:-

 “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.”

Extrapolating to humans, the researchers think that a combination of L. reuteri with the tryptophan-rich diet would generate a more tolerant, less inflammatory gut environment. Improvements in IBS management could mean many around the world that suffer such gut issues including diarrhoea would experience considerable relief.

In more general terms, any nutritionist will tell you that you must get your daily protein requirement which is 46 grams for an average woman and 56 grams for men. The highest quality of protein includes all the essential amino acids and is bio-available to the human body. Of all the essential amino acids, their are four critical for strength and recovery – Valine, Leucine, Isoleucine and Glutamine.

Cervantes-Barragan, L., Chai, J.N., Tianero, M.D., DiLuccia, B., Ahern, P.P., Merriman, J., Cortez, V.S., Caparon, M.G., Donia, M.S., Gilfillan, S., Cella, M., Gordon, J.I., Hsieh, C.-S., Colonna, M. (2017) Lactobacillus reuteri induces gut intraepithelial CD4+CD8 alpha alpha+ T cells. Science. Aug. 3 DOI: 10.1126/science.aah5825 see the paper.