New research identifies a link between diet, gut bacteria and the immune system

17 May, 2018
  • Researchers were able to trace a set of interactions that help explain how diet and the gut bacteria influenced by diet may act on the immune system to limit inflammation and nerve damage in mice.
  • The team also found preliminary evidence verifying that similar interactions affect human cells.
  • The study, supported by the International Progressive MS Alliance and others, provides important clues for better understanding the gut-brain connection and could lead to new treatment approaches for MS.
  • The international team, led by Dr Francisco Quintana (Brigham and Women’s Hospital, Harvard Medical School) published their findings in the journal Nature online on May 16, 2018.

MS is a complex disease that arises when the immune system mistakenly attacks and inflames areas of the brain and spinal cord. What causes a person’s immune system to turn on their own body has not been fully revealed, but it is believed to be due to a complex interaction between a person’s genetic and environmental factors. Read more about these factors here.

Diet is one of the environmental factors that may influence our risk of developing MS, and there is growing research interest in the role that our gut bacteria may play in mediating the effect of our diet on our health. Our small and large intestines contain millions of bacteria. These bacteria help us digest our food and they also play a critical role in signalling to our immune systems. Recent studies have also revealed that there are differences in the gut bacteria from people with MS compared to people without MS.

The effects of diet on gut bacteria and on immune system activity is difficult to tease out, and much is not yet understood. Dr Francisco Quintana and an international team of collaborators set out to understand the links between immune activity and diet by studying mice with an MS-like disease. They looked at how dietary components are processed by gut bacteria, and how these interactions influence the activity of cells within the brain and spinal cord. This work was supported by the International Progressive MS Alliance, of which MS Research Australia is a managing member.

This study published this week in one of the most prestigious scientific journals Nature, focused on possible interactions between gut bacteria and glial cells, the support cells of the brain and spinal cord. Glial cells are the most abundant cells in the brain and spinal cord and play major roles in both health and disease. Specifically, the study focused on the interactions of two of these types of cells: microglia and astrocytes.

Microglia provides support for nerve cells and also act as immune cells in the brain by locating microscopic foreign invaders and ‘eating’ them. Astrocytes perform many functions, including providing nutrients and signals to the surrounding cells.

The scientists discovered, that in a laboratory model of MS, astrocytes appeared to play a key role in the disease process and so they looked more closely at the signals going to the astrocytes from the microglial cells. They discovered that the microglia can send both positive and negative signals to the astrocytes, which could enhance or decrease the inflammation caused by the astrocytes.

When they looked more closely at what might determine whether the microglia send anti-inflammatory or inflammatory signals to the astrocytes, they discovered a key role for a molecule generated by our gut bacteria.  When gut bacteria break down tryptophan, an amino acid we get through our diets, it releases a molecule that can travel to the brain and influence the activity of the microglia. The molecule switches the microglia to release more anti-inflammatory signals and reduces the inflammatory activity of the astrocytes, resulting in less severe MS-like illness in the mice.

This is the first time that a dietary metabolite or byproduct produced by gut bacteria has been shown to travel through the body and directly affect cells in the brain and spinal cord.

The team also found preliminary evidence that similar interactions influence human cells. They now plan to continue this line of research to identify therapies or probiotics that can reduce inflammation to turn off or decrease disease activity in people with MS.

Identifying components of this ’gut-brain‘ connection and better understanding this complicated web of interactions between the immune system and the brain provides important clues that could lead to new treatment approaches for MS and other neurodegenerative disorders like Alzheimer’s disease and glioblastoma.

’These findings are just the beginning of what we expect will be major progress toward understanding underlying mechanisms and finding new treatments for people living with progressive MS.’ said Professor Alan Thompson, Chair of the Alliance’s Scientific Steering Committee and Dean of University College London Faculty of Brain Sciences.

A statement from the International Progressive MS Alliance can be found here.

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