The link between gut bacteria and autoimmune disease
New research suggests gut bacteria may be linked to autoimmune diseases, such as rheumatoid arthritis and Type 1 diabetes.
Overview
This is the last entry in our three-part series on gut bacteria and its impact on other parts of the body. We hope you’ve enjoyed this series- let us know what you think in the comments!
One of the many ways in which microbes residing in the gastrointestinal tract benefit the body is by regulating the body’s immune system.
A change in the gut microbiota can cause immune dysregulation, and this can lead to autoimmune disorders, a class of disorders in which the body’s immune system attacks healthy cells.
The gut microbiota does not only regulate the intestinal immune system. It also has a significant role in adaptive immunity, the process by which the body eliminates a pathogen and creates immunological memory to have an enhanced response to that pathogen in the future. The role of gut microbes in shaping both adaptive immunity and innate immunity has been revealed by recent advances in next-generation genome sequencing technology and the development of germ-free mouse models.
Recent studies have unraveled the role of gut bacteria in both intestinal and extra-intestinal autoimmune disorders.
Inflammatory Bowel Disease (IBD) is an innate autoimmune disease that affects the gastrointestinal tract. Recent studies have shown that the microbial environment in patients with IBD greatly differs when compared to that of a normal adult. This suggests that intestinal inflammation is a major cause of microbial imbalances in patients with IBD and that a disturbance in the gut microbiota may result in immunological dysregulation, which underlies disorders such as IBD.
Another important autoimmune disease is Type 1 diabetes. This disease results from T-cell mediated destruction of insulin-producing cells in the pancreas. T-cells, which are the key component of the adaptive immune system can differentiate into four major subtypes, including regulatory T cells (Treg). Treg is a mediator of immune tolerance, and its dysfunction can lead to autoimmune disease. A significant reduction of intestinal Treg was observed in patients with Type 1 diabetes, suggesting the involvement of gut microbiota in the disease.
Imbalances in gut microbiota can also cause adaptive autoimmune disorders. Recent studies with germ-free mouse models suggest that gut microbes have a role on the severity of rheumatoid arthritis, a disease that causes inflammation of the joints and affects approximately 1% of the world’s population.
Signals from gut microbes can affect diseases in other areas of the body by regulating systemic immune components. The mechanism by which this happens is not clear, but it may be mediated by the circulation of microbiota-derived soluble factors from the gut to other areas of the body. This can be caused by genetic factors, as well as environmental factors, such as overuse of antibiotics.
An important next step for researchers in this space is to determine whether changes in gut microbiota are the cause of autoimmune diseases or are a result of the diseases themselves.
Researchers have also seen that a single new bacterial species within the gut can have a drastic impact on host immunity and pathology. Scientists are currently looking into how microbiota composition varies under different conditions and how this can impact autoimmune disease.
Further Reading
L. Wen, et al. Nature, 2008, 455(7216):1109–1113.
SK Mazmanian, JL Round, and DL Kasper. Nature, 2008, 453(7195):620–625.
WS Garrett, et al. Cell, 2007, 131(1):33–45.
HJ Wu, et al. Immunity, 2010, 32(6):815–827.
Hsin-Jung Wu and Eric Wu. Gut Microbes, 2012, 3(1):4–14.
RH Nanjundappa, Cell, 2017, 171(3):655–667.
