New research suggests we may one day be able to vaccinate against depression, reducing suffering.
Key facts:
- Depression is linked to inflammation in the body and brain. Anti-inflammatory treatments improve depression.
- Environmental factors like lack of contact with “old friends” (microbes we coevolved with) are increasing inflammation and depression.
- Probiotics, helminths and vaccines that restore regulatory immune cells could treat or prevent depression by reducing inflammation.
- Transient inflammation briefly improves mood through effects on serotonin. Sustained inflammation worsens mood.
- T cells that travel to the brain may regulate inflammation there and influence depression. Vaccines inducing these cells could help.
The Link Between Inflammation and Depression
Depression is one of the most common mental health disorders today.
Scientists have discovered important links between depression and inflammation (the immune system).
Many depressed people have higher levels of inflammatory markers like C-reactive protein and cytokines.
These chemical messengers of inflammation are produced by the immune system.
What causes this inflammation? Factors like stress, lack of exercise, obesity, and medical disorders can promote it.
Importantly, reducing inflammation improves depressive symptoms. Antidepressant treatments lower inflammatory markers.
This suggests chronic inflammation may directly contribute to depression in some individuals. Inflammatory signals to the brain likely interfere with mood regulation.
How Environmental Changes May Increase Depression
Interestingly, depression rates appear to be rising worldwide along with other inflammatory disorders like allergies and autoimmune diseases.
Some scientists believe this is due to changes in lifestyle and environment.
In particular, we have far less exposure to “old friends”- microbes and parasites our ancestors evolved with over millennia.
These organisms helped train and regulate the immune system.
Loss of old friends may lead to faulty immune regulation and increased inflammation.
Urban populations have higher rates of depression than rural ones.
People moving from developing to developed countries also show increased depression risk.
This implicates industrialized, urban lifestyles in the depression epidemic.
Using Microbes to Treat or Prevent Depression
If inflammation drives depression, reducing inflammation may prevent or improve it.
Scientists are now exploring whether probiotics, helminths (parasitic worms) or other microbes could restore proper immune regulation.
Early studies show some promising results. For example, probiotics like Bifidobacterium infantis reduce depressive behaviors and inflammation in animal experiments.
Helminths are also strong immune regulators and can treat diseases like colitis.
Testing whether they improve depression in clinical trials is a logical next step.
Vaccines Made From Microbes: Mycobacterium vaccae
Vaccines utilizing immune-regulating microbes may one day prevent or treat depression.
The microbe Mycobacterium vaccae shows encouraging results.
M. vaccae is an “old friend” found in mud that increases anti-inflammatory regulatory T cells.
In cancer and allergy trials, patients receiving vaccines of killed M. vaccae reported improved quality of life.
This was likely due to its immune effects reducing depressive symptoms.
More research is still needed, but microbe-based depression vaccines show great promise for a condition desperately needing better treatments.
The Dual Effects of Inflammation on Mood
Inflammation has different effects on mood depending on how long it lasts.
Acute short-lived inflammation briefly improves mood by activating serotonin neurons involved in regulating emotions.
For example, flu infections with high inflammation often cause mild, transient depression improvement.
This is because inflammatory chemicals stimulate specific serotonin-releasing nerve cells.
However, chronic long-term inflammation has the opposite effect, worsening mood and increasing depression risk.
Vaccines utilizing acute inflammation may one day lift moods short-term.
Avoiding chronic inflammation is crucial for long-term mental health.
Harnessing the Brain’s Immune Cells
The brain contains its own immune cells as part of the neuroimmune system.
Recently, scientists discovered specialized anti-inflammatory T cells travel to the brain and help regulate inflammation there.
In experiments, activating these cells reduced brain inflammation and improved symptoms in neuroinflammatory disorders like multiple sclerosis.
Some even recognize and respond to brain molecules.
It may be possible to develop vaccines inducing more of these protective brain immune cells.
Early research suggests they could dampen neuroinflammation in depression.
Much more work is needed to explore this approach.
The Future of Depression Treatment
Depression remains difficult to treat and affects millions globally. Exciting new research implicates immune inflammation in contributing to some forms of depression.
Environmental factors increasing inflammation like lack of old friends may help explain rising depression rates.
Correcting this imbalance using probiotics, helminths or microbial vaccines to reduce inflammation shows real promise for preventing and treating depression.
More clinical trials are needed, but regulate the immune system may be the key to defeating depression in the future.
The studies provide hope we can one day vaccinate against depression.
References
- Study: Can we vaccinate against depression?
- Authors: Graham A W Rook (2012)
