60 second summary
- Inflammation is present in all mental health conditions
- Increased cases of inflammation are thought to be because of decreased exposure of our immune system to microbes ~ the hygiene hypothesis
- Mycobacterium vaccae is known to regulated metabolism of molecules associated with mood so could be administered as a therapeutic drug for mood related disorders
In an arduous search for the root cause of a group of common conditions scientists look at the diseases’ common denominators, so symptoms, genes or even lifestyle choices that all individuals share. In terms of mental health disorders inflammation has unveiled itself as a trait shared by all- from obsessive cumpulsive disorder to depression.
Inflammation- process by which the body’s white blood cells and substances they produce protect us from infection with foreign organisms, such as bacteria and viruses.
Over the past few years there has been increased interest in vaccinating individuals with depression which affects approximately 300 million people worldwide. It has been clear to many scientists now that the body and the mind can be tightly linked in dangerous feedback loops.
How could such a vaccination be possible?
Research has found a causal link between depression and increased levels of pro-inflammatory cytokines and tight association between inflammation and mental health issues- simply put:
Inflammation causes mental health issues, and mental health issues themselves provoke inflammation.
Cytokine- derived from the Greek words “cyto”- cell and “kinos” – movement, these molecules are crucial in immune signaling and activating responses to inflammation and infections.
The importance of developing treatments for depression are more important than every before- from 2005-2015 cases of depression increased by nearly a 20%.
Why has depression and inflammation been on the rise?
One of the main suggestions is the “old friends hypothesis” which explains that in our hygiene obsessed world today we have significantly decreased exposure to mud, dirt and large varieties of microbes. Studies in mice which have born without any exposure to bacteria have been shown to have poorly developed lymphoid systems and are susceptible to inflammatory disorders.
Lymphoid system-network of structures in body important in the removal of toxins and waste
For our immune system to respond adequately to threats it must be educated when we are young , such as by exposure to dirt. Studies have even confirmed that children raised in farms or those with pets are less likely to develop allergies and asthma.
The science- If you allow your body to be exposed to certain pathogens your body’s adaptive immune system reacts and expands its regulatory T cell (Treg) population which are important in supressing other immune cells . For instance B. Fragilis, found in stool and a normal part of the gut microbiome releases a chain of sugars polysaccharide that directly increases Tregs and so restrains activity of immune response inducing cells such as Th17..
M vaccae and the gut
In the 1970’s a research team were trying to figure out why vaccinations for leprosy were more effective in certain area more than others. What they found was that there areas were more abundant in a microbe called Myobacterium vaccae, which naturally originates in soil and was shown to boost the effectiveness of the vaccine. Furthermore in another trial, when administered to cancer patients alongside chemotherapy, these individuals experienced a significant increase in quality of life, despite not living ay longer than the controls just on chemo.
How does M vaccae work?
The science- In mice experiments M vaccae has been shown to increase serotonin metabolism which is a neurotransmitter in the brain associated with mood regulation. This suggests that ingesting the microbe upregulates serotogenic neurons that modulate stress behaviours.
Despite not being part of today’s normal human microbiome, introduction of this microbe into the body may have significant beneficial effects in terms of immunity and inflammation. It is likely that M vaccae was a resident of the gut microbiome of our ancestors due to their exposure to dirty mud and water. Therefore long term exposure of this microbe is suggested to trigger responses in our adaptive immune system and develop a tolerance to responses in stressful situations. 
Overall this research is of great importance and has huge future potential in terms of prevention and treatment of psychiatric disorders.
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 Psychology Today. (2017). Depression Is Not a Choice. [online] Available at: https://www.psychologytoday.com/us/blog/teen-angst/201704/depression-is-not-choice [Accessed 18 Jul. 2019].
 News Medical. (n.d.). What are Cytokines?. [online] Available at: https://www.news-medical.net/health/What-are-Cytokines.aspx [Accessed 18 Jul. 2019].
 The Guardian. (2018). What is depression and why is it rising?. [online] Available at: https://www.theguardian.com/news/2018/jun/04/what-is-depression-and-why-is-it-rising [Accessed 18 Jul. 2019].
 Can we vaccinate against depression?. (2012). [ebook] Available at: [Accessed 18 Jul. 2019].
 Ingestion of Mycobacterium vaccae decreases anxiety related behaviour and improves learning in mice. (2013). [ebook] Available at: [Accessed 18 Jul. 2019]. e(Ii(t)