Researchers found that early in life intestinal microorganisms “educate” the thymus to develop T cells; findings could lead to improved immune system therapeutics and associated clinical laboratory tests
Researchers at the University of Utah and the Sloan Kettering Institute (SKI)—the experimental research division of the Memorial Sloan Kettering Cancer Center (MSKCC) in New York—have uncovered new insights into how the immune system learns to distinguish between harmful infectious bacteria and “good” bacteria in the microbiome that occupies the gastrointestinal tract.
The researchers published their findings in Nature. They used engineered mice as the test subjects and say the study could lead to a greater understanding of human conditions such as Type 1 and Type 2 diabetes and inflammatory bowel disease (IBD). In turn, this new knowledge could lead to new diagnostic tests for clinical laboratories.
“From the time we are born, our immune system is set up so that it can learn as much as it can to distinguish the good from the bad,” Matthew Bettini, PhD, Associate Professor of Pathology said in a University of Utah news release.
Does Gut Bacteria ‘Educate’ the Immune System?
The researchers were attempting to learn how the body develops T cells specific to intestinal microorganisms. T cells, they noted, are “educated” in the thymus, an organ in the upper chest that is key to the adaptive immune system.
“Humans and their microbiota have coevolved a mutually beneficial relationship in which the human host provides a hospitable environment for the microorganisms and the microbiota provides many advantages for the host, including nutritional benefits and protection from pathogen infection,” they wrote in their study. “Maintaining this relationship requires a careful immune balance to contain commensal microorganisms within the lumen, while limiting inflammatory anti-commensal responses.”
Findings Challenge Earlier Assumptions about Microbiota’s Influence on Immunity
The researchers began by seeding the intestines of mice with segmented filamentous bacteria (SFB), which they described as “one of the few commensal microorganisms for which a microorganism-specific T-cell receptor has been identified.” In addition, SFB-specific T cells can be tracked using a magnetic enrichment technique, they wrote in Nature.
They discovered that in young mice, microbial antigens from the intestines migrated to the thymus, resulting in an expansion of T cells specific to SFB. But they did not see an expansion of T cells in adult mice, suggesting that the process of adapting to microbiota happens early.
“Our study challenges previous assumptions that potential pathogens have no influence on immune cells that are developing in the thymus,” Bettini said in the news release. “Instead, we see that there is a window of opportunity for the thymus to learn from these bacteria. Even though these events that shape which T cells are present happen early in life, they can have a greater impact later in life.”
For example, T cells specific to microbiota can also protect against closely related harmful bacteria, the researchers found. “Mice populated with E. coli at a young age were more than six times as likely to survive a lethal dose of Salmonella later in life,” the news release noted. “The results suggest that building immunity to microbiota also builds protection against harmful bacteria the body has yet to encounter.”
According to the researchers, in addition to protecting against pathogens, “microbiota-specific T cells have pathogenic potential.” For example, “defects in these mechanisms could help explain why the immune system sometimes attacks good bacteria in the wrong place, causing the chronic inflammation that’s responsible for inflammatory bowel disease,” they suggested.
Other Clinical Laboratory Research into the Human Microbiome
The research conducted by the University of Utah, Sloan Kettering Institute, and others, adds to a growing understanding of the human microbiome. For example, in “International Study into Ancient Poop Yields Insight into the Human Microbiome, May Produce Useful Insights for Microbiologists,” Dark Daily reported on an international study of 2000-year-old human feces which suggested that the microbiomes of today’s humans may have been modified by modern phenomena such as processed food and sanitation.
And in “Harvard Medical School Study Finds ‘Staggering’ Amounts of Genetic Diversity in Human Microbiome; Might Be Useful in Diagnostics and Precision Medicine,” Dark Daily reported on a study from Harvard Medical School and Joslin Diabetes Center that unveiled a “staggering microbial gene diversity” in the microbiome and the potential for identification of more-useful biomarkers for disease detection.
And a study from the University of Nebraska-Lincoln and the Ocean Road Cancer Institute in Tanzania raised the possibility that bacteria in the cervical microbiome could lead to new tests for cervical cancer. (See Dark Daily, “University Study Suggests Cervical Microbiome Could Be Used by Medical Laboratories as Biomarker in Determining Women’s Risk for Cervical Cancer.”
All of this suggests the potential in the future “for clinical laboratories and microbiologists to do microbiome testing in support of clinical care,” said Robert Michel, Editor-in-Chief of Dark Daily and its sister publication The Dark Report. Of course, more research is needed in these areas.
“We believe that our findings may be extended to areas of research where certain bacteria have been found to be either protective or pathogenic for other conditions, such as Type 1 and Type 2 diabetes,” Bettini said in the University of Utah news release. “Now we’re wondering, will this window of bacterial exposure and T cell development also be important in initiating these diseases?”