One reason runaway inflammation happens is that the immune system has lost its way. A surprising potential explanation for why this can happen is emerging: Our immune systems could be missing exposure to some crucial things that aid in its healthy development: bacteria and viruses, and parasitic worms—the very things it is designed to ward off. The loss of exposure to these microbial organisms due to our modern diets, medications, and lifestyles could be producing naive and untrained immune systems that have a tendency to go haywire.Inflammation seems to cause mental health issues, and mental health issues themselves provoke inflammation, creating a dangerous feedback loop.
Soil bacteria's effects on inflammation are easily seen in a phenomenon called the "farm effect." Studies show that interacting with the land and being around farm animals is protective against inflammatory conditions like asthma and allergies. For children who don't live on farms, simply having pets or coming into contact with cats and dogs can similarly lower the risk of allergies. Rook thinks the farm effect can be explained by the animals bringing in microbial life on dirty paws and bodies, which then helps to train the immune system.A recent study led by Stefan Reber at the University of Ulm in Germany revealed a connection between good emotional health and growing up around dirt. Forty men were brought to the lab and put through a stress test, where they had to give a speech in front of steely-faced scientists in white coats. The ones from rural environments reported feeling stressed, but it was the ones who grew up in cities who had a massively exaggerated inflammatory response. Their inflammation lasted for the whole length of the study.“There's something out there, something that we need to meet in the earth," Rook said.In the 1970s, Rook and an immunologist, John Stanford, pulled M. vaccae out from the mud near Lake Kyoga in Uganda. They were trying to figure out why vaccinations for leprosy were more effective in certain countries when they came across M. vaccae—a bacteria closely related to leprosy that was possibly boosting the effect of the vaccine.A surprising potential explanation for runaway inflammation: Our immune systems could be missing exposure to enough bacteria, viruses, and parasitic worms.
Lowry first injected mice with M. vaccae shortly after, in 2007. He saw increases in serotonin metabolism in the prefrontal cortex, a neurotransmitter and part of the brain linked with mood and personality. Another study in mice found that when the animals were put with a large aggressive male, the ones injected with M. vaccae behaved less anxiously, and were less likely to develop inflammatory issues like colitis. In a more recent study in rats, Lowry and his colleagues found that animals that had been given M. vaccae had faster fear extinction—they were able to get over something they had been conditioned to be afraid of more quickly."That's what individuals with anxiety or PTSD can't do, is extinguish fear," Lowry said. "Even in safe environments."People who had higher levels of inflammation were more likely to be depressed about 12 years later.
Lowry had been cautious about his lab's findings, especially since the team had mostly done experiments in animals. But simultaneously, evidence continued to mount in humans that matched their findings—that inflammation wasn't just associated with mental health disorders, but was causing them.By measuring levels of inflammatory molecules in blood, researchers were finding they could predict mental health issues later. In 2010, people working in U.K. government offices who had higher levels of inflammation were more likely to be depressed about 12 years later. In 2014, another U.K. study looked at 15,000 children around 9 years old and found that those who were not depressed but showed raised inflammation were more likely to be depressed a decade later. And a study from 2014 done by the U.S. Marines found the percentage of soldiers who got PTSD was greater in those who had raised levels of inflammatory molecules in their blood before they went to combat.
“In other words, if you have a propensity for high inflammatory function, then that in fact is the deciding factor on whether or not the individual goes on to develop these anxiety and depressive-like syndromes,” Lowry said.Chronic inflammation affects our whole bodies, including the brain. Inflammation can interfere with the way the brain functions, altering neurotransmitters to the behavior of synapses, the connections between neurons. The brain also has its own immune system which, when overly active, can lead to persistent neuro-inflammation. M. vaccae could stop the neuro-inflammatory response of the brain's immune cells in rats, and the associated negative behavioral changes that came along with it.In May of this year, Lowry, Rook and others found a single molecule from M. vaccae that has anti-inflammatory effects in human and mouse cells. It's a lipid—a fat molecule—with a very specific chemical shape. Mammals can't make it.In mice, the molecule binds to a receptor that triggers a shutting off of various inflammatory processes. This likely evolved so that a disease-causing bacteria could turn off a host’s immune system and take over. But in non-threatening bacteria, it’s actually a form of ecological service, Lowry said, helping our immune systems cool off instead of running on overdrive all the time.Cancer patients given the soil bacteria M. vaccae had increased levels of emotional health, cognitive functions, and decreased pain.
Not every case of depression is caused by inflammation. But figuring out the cases where inflammation is playing an overwhelming role can bring us closer to understanding the best treatment options, said Jane Foster, a neuroscientist at McMaster University who studies the immune system.Regardless of what happens next, the causal role of inflammation and mental health issues forces us to rethink the underlying cause of mental health disorders. The changing environments in which we live could be altering the ways our bodies function and dramatically affecting the way we feel. This brings us a long way from what used to be a prevailing dogma: that the mind and body are separate, and so are their illnesses.To Cryan, these kinds of microbial approaches are reason for optimism. “Unlike our genomes, which we can't do much about except blame our parents and grandparents, our microbiomes are potentially modifiable,” he said. “That gives us a little bit more, and also gives the individual more agency over their own health.”Follow Shayla Love on Twitter.Sign up for our newsletter to get the best of VICE delivered to your inbox daily.This is just one way our futures will likely involve microbes as medicine for mental health.