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
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.”
Matthew Bettini, PhD (left), Associate Professor of Pathology at the University of Utah, co-authored the study along with Gretchen Diehl, PhD (right), an immunologist at Sloan Kettering Institute. The team also included researchers from the Baylor College of Medicine in Houston and the Washington University School of Medicine in St. Louis. “Our studies make clear that there is a window in which gut microbiota have access to the immune education process. This opens up possibilities for designing therapeutics that can influence the trajectory of the immune system during this early time point,” Bettini said in the University of Utah news release. (Photo copyright: University of Utah/Sloan Kettering Institute.)
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
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?”
Is gut microbiota the fabled fountain of youth? Researchers at Valenzano Research Lab in Germany found it works for killifish. Could it work for other vertebrates as well?
Research into the microbiomes of humans and other animals is uncovering tantalizing insights as to how different microbes can be beneficial or destructive to the host. It is reasonable to expect ongoing research will eventually give microbiologists and clinical laboratories useful new medical laboratory tests that assess an individual’s microbiome for diagnostic and therapeutic purposes.
Human microbiota (AKA, microbiome) have been identified as having a key role in several different health conditions. In previous ebriefings, Dark Daily reported on several breakthroughs involving the microbiome that bring the promise of precision medicine ever closer. Research and clinical studies are contributing to more accurate diagnoses, identification of best drugs for specific patients, and, enhanced information for physician decision-making, to name just a few benefits.
Valenzano Lab published its study online in August. The team of scientists and researchers led by Dario Valenzano, PhD, focused on the longevity of the turquoise killifish (Nothobranchius furzeri), a tiny fish native to the African countries of Mozambique and Zimbabwe. They found that when older killifish ate the fecal matter of younger killifish they lived longer. The fecal matter carried the microbiota to the older fish and extended their lifespans.
Moving Microbiome from One Gut to Another
To perform the research, Valenzano and his team first treated killifish that were nine and a half weeks old (considered middle-aged) with antibiotics to cleanse their gut flora. The fish were then placed in a sterile aquarium containing the gut contents of young adult killifish that were just six weeks old. Although killifish won’t typically eat feces, they would nip at the gut contents in the water and swallow some of the microbes from the younger fish in the process. The researchers discovered that the transplanted microbes were able to successfully colonize the stomachs of the older fish.
Dario Valenzano, PhD (above), gazes at an older Killifish, the subject in his research into increased aging at the Valenzano Research Lab in Cologne, Germany. Studies of the microbiomes of different species is expected to eventually give microbiologists new and useful clinical laboratory tests. (Photo copyright: Max Planck Institute for Biology of Aging.)
When the middle-aged killifish reached the age of 16 weeks—considered elderly—their gut microbiomes were still similar to that of a six-week-old fish. The process had a noticeable effect on the lifespan of the killifish that received the microbiome transplants from the young fish. They lived 41% longer than killifish that received microbes from middle-aged fish and their longevity increased by 37% over fish that were not exposed to any treatment at all. In addition, at 16 weeks, the killifish who had received the transplants were much more active than fish of the same age who had not received the transplants.
“These results suggest that controlling the composition of the gut microbes can improve health and increase life span,” the study paper noted. “The model system used in this study could provide new ways to manipulate the gut microbial community and gain key insights into how the gut microbes affect aging. Manipulating gut microbes to resemble a community found in young individuals could be a strategy to delay the onset of age-related diseases.”
Transferring Fecal Microbiota to Save/Extend Human Lives
Previous research has indicated there may be a connection between microbiomes and aging in some animals, and that the diversity of gut microbes decreases with age. This study proved that this same pattern is true in turquoise killifish.
However, Valenzano does not know how the microbes are affecting the lifespans of the older killifish. “It is possible that an aging immune system is less effective at protecting the micro-organisms in the intestines, with the result that there is a higher prevalence of pathogens in older guts. The gut microbiota in a young organism could help to counter this and therefore support the immune system and prevent inflammation. This could lead to longer life expectancy and better health,” he stated in a press release.
“You can really tell whether a fish is young or old based on its gut microbiota,” Valenzano told Nature. He noted, however, that it is too early to determine if fecal transplants can be used in humans to extend life. “I wouldn’t go that far. This is really early evidence that this has a potential positive effect.”
There is, however, a similar procedure used in humans called Fecal Microbiota Transplant or FMT that has demonstrated promising results in treating certain illnesses.
In a fecal transplant, fecal matter is collected from an approved donor, treated, and placed in a patient during a colonoscopy, endoscopy, sigmoidoscopy, or enema. The purpose of the transplant is to replace good bacteria in a colon that has undergone an event that caused the colon to be inundated with bad bacteria, such as Clostridium difficile, resulting in C. diff. infection, a life-threatening illness that, according to the Centers for Disease Control and Prevention (CDC), kills tens of thousands of people each year.
“The challenge with all of these experiments is going to be to dissect the mechanism. I expect it will be very complex,” stated Heinrich Jasper, PhD, in the Nature article. Jasper is a professor at the Buck Institute for Research on Aging in Novato, California. His lab is working on similar research with microbiome transplants in fruit flies. He predicts this type of longevity research will be performed on other animals in the future.
Valenzano’s and Jasper’s research may eventually create new diagnostic tools for microbiologists to assess the microbiome of individual patients. This technology may also enable microbiologists to advise pathologists and clinical laboratories regarding what specific microbes may be harmful and what microbes may be therapeutically beneficial to patients.
