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Go to CuriosityStream.com/SciShowPsych to start streaming thousands of documentaries and nonfiction TV shows. [♪ INTRO]. Our immune system is an interconnected network of organs, proteins, and cells that protects our bodies from all the things that can make us sick.

In other words, it’s the biological equivalent of Gandalf the Grey, telling germs “you shall not pass!” So yeah, it’s pretty critical to our physical health. But it turns out it might play a big role in our mental health, too. And by understanding the connections between our immune systems and our brains, we can start developing more effective treatments for mental health conditions, and help destigmatize them in the process.

This entire field of research, now called psychoneuroimmunology, really began in the 1980s, when some clever experiments revealed that activating somewhat random parts of the brain, like the sense of taste, could influence immune reactions. That led to a flurry of studies on how brains can affect immune health. And, over time, scientists realized the relationship was more of a two-way street.

So nowadays, we have the subfield of immunopsychiatry, which focuses on the ways our immune systems affect our brains. And that research is increasingly supporting the idea that immune reactions like inflammation can cause or perpetuate mental health conditions. Inflammation happens when your immune system springs into action.

Basically, it’s when white blood cells, which are essentially the body’s… ya know, like bodyguards, swarm to an area that needs protection from germs, like an infection site, or a wound. Calling in the white blood cell cavalry can cause swelling and pain, and it increases the blood flow to the area, which tends to make it warmer and redder! All of which was apparently reminiscent enough of fire that old-timey doctors called this inflammation.

Now, inflammation is usually a sign that your immune system is doing its job. And it’s not a big deal if it’s acute, or temporary. I mean, the soreness of a scraped knee or swollen bug bite is definitely uncomfortable, but it means your body is healing, and it goes away fairly quickly.

Sometimes, though, inflammation goes on much longer. Chronic inflammation can stick around for months, or even years. And it can happen even though there’s no real enemy there to fight!

All too often, chronic inflammation stems from an autoimmune condition, where the immune system just kind of starts attacking parts of the body. And this is where immunopsychiatry really comes into play, because it turns out that chronic, autoimmune-related inflammation might underlie a lot of mental health conditions, including depression, anxiety, and even psychosis. For instance, in 2013, a nationwide study of around 3.6 million people in Denmark found that those that were diagnosed with an autoimmune disorder were 45% more likely to be diagnosed with a mood disorder later.

And in a 2018 meta-analysis which included more than 25 million people, researchers found a positive association between being diagnosed with psychosis and having an autoimmune condition, even when they only considered autoimmune conditions that don’t affect neurons directly, like celiac disease or psoriasis. There are also clues coming from a treatment standpoint, as inflammation seems to make medications like antidepressants less effective. This effect is so notable that scientists have even been looking into whether drugs which target immune signaling molecules called cytokines might help treat mental disorders in patients with higher levels of inflammation.

In fact, experts are starting to think targeting the immune system alone might be enough to treat certain mental health conditions. For instance, a 2019 meta-analysis found that nonsteroidal anti-inflammatory drugs might be an alternative for treating major depression and schizophrenia. But, these treatments are still in the research phases, and the drugs definitely haven’t proven effective in clinical trials yet.

Plus, they can carry serious risks, like the increased possibility of heart attacks, strokes, and kidney damage. So while we’re learning a lot about about how inflammatory immune responses can affect our mental health, these new treatments aren’t ready for primetime. And even if they were, it’s worth remembering that any potential treatment plan should be discussed with a medical professional, as your unique brain and body need to be factored in!

Immunopsychiatry researchers are now trying to pin down exactly how the immune system has such a big impact on the brain, as that could lead us to safer, more effective options. That seems to come down to how proteins and other chemicals used by the immune system affect brain cells. For instance, in a study published in Psychopharmacology in 2015, researchers examined whether the proteins present in long-term, low grade inflammation could predict whether someone would experience persistent depression symptoms. 656 participants who’d been diagnosed with depression had their blood tested for several markers of inflammation.

This included the interleukin-6, or IL-6, which is a molecule used by the immune system to signal that a response is needed, and which plays a key role in chronic inflammation. And it also included C-reactive protein, a protein that’s made by your liver and increases when there’s inflammation in your body. Then, they tested everyone again five years later.

And the scientists found that people with consistently elevated levels of both proteins were more likely to experience persistent depression. In fact, both IL-6 and C-reactive protein successfully predicted long-term depression symptoms regardless of a person’s age, gender, weight, smoking history, health status, and socio-economic demographic. Other research has connected IL-6 specifically to schizophrenia.

In a 2020 study of over 5,400 Finnish people, 31-year-old people with schizophrenia had more than twice as much IL-6 in their blood! Of course, more research is needed to figure out exactly what’s happening at the molecular level. Like, whether IL-6 is causing changes to neurons on its own, or is acting as an indicator of something else going on.

That will tell drug developers precisely what to go after. In the meantime, the continued deepening of our understanding of how mental health conditions can stem from our bodies could go a long way towards reducing social stigmas. Though many of us have been taught that psychological issues aren’t linked to the rest of our bodies, we know now that just isn’t true.

Physical changes can affect how our brains work, and psychological issues can change our bodies. The connection between the immune system and the brain is just one example. And destigmatizing mental illness can encourage people to get help today while we wait on the treatments of tomorrow!

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