This Is How Your Immune System Influences Your Mental Health

In the past, it was taught and accepted that the brain was the only organ in the human body that was “immune privileged” meaning it lacked any direct physical connection to the immune system. In 2015, one experiment at the University of Virginia School of Medicine overturned that idea in what was called “one of the ten most important scientific breakthroughs of the year” by Science magazine. Other researchers around the world have since replicated and corroborated the findings. They literally have to rewrite the textbooks.

What scientists discovered is that there is, in fact, a network of lymphatic vessels in the human brain. It turns out that the brain is like all other tissue in the human body and is connected to the peripheral immune system through meningeal lymphatic vessels. This discovery gave scientists a better understanding of the workings of the brain and an entirely new avenue for treating neurologic and immune disorders. This necessitates that neurological disorders, from depression and Alzheimer’s to multiple sclerosis and autism, must be reconsidered.

The Brain’s Lymphatic System

The lymphatic system is your body’s ambulance and trash collection service all in one. When you cut yourself, it rushes immune cells to the site to fight any foreign intruders that might cause infection. It also carries away the resulting cellular debris and disposes of it. In autoimmune disorders, like rheumatoid arthritis, lupus, or MS, the immune system becomes overactive, and immune cells attack healthy tissue.

The discovery of lymphatic vessels in the brain raises a number of questions both about the workings of the brain and the diseases that originate there. Could it be that the same thing that happens in autoimmune disorders in the body is happening in the brain? Is the immune system triggering immune cells in the brain, called microglia, to become overactive resulting in neuroinflammation or eating away at synapses? In a brain with Alzheimer’s, abnormal levels of naturally occurring proteins clump together to form plaques that collect in and between neurons and disrupt cell and synaptic function. Are the proteins accumulating because they’re not being efficiently removed by the lymphatic vessels?

At the moment, we don’t know the answer to these questions yet. However, it is possible that the lymphatic vessels play a major role in all neurological diseases.

Two important implications

There are two main takeaways from this finding:

• The brain is an immune organ full of immune cells, called microglia, that affect function and health.
• The brain is physically connected to and engaged in a constant dialogue with your body’s immune system.

According to the book, The Angel and The Assasin, by Donna Jackson Nakazawa:

The work of this small band of researchers and the discovery of microglia’s powers have given science an entirely new unifying theory of brain-related disease:

1. 1. 1. 1. 1. 1. A (Microglia are the white blood cells of the brain) +
               2. B (The body’s immune cells directly communicate with the brain through tiny vessels that bridge the body and brain) =
               3. C (Anything that triggers disease in the body can easily influence the immune system in the brain and trigger disease there too.) “

Inflammation in Your Brain

Inflammation is a natural and healthy immune system response to environmental irritants, toxins, and infection. When the immune system is activated by a threat, pro-inflammatory hormones signal white blood cells to rush in and clean up the infected or damaged tissue. Once the invaders have been defeated, anti-inflammatory agents then move in to begin the healing process. In a normal immune system, a natural balance exists between inflammation and anti-inflammatory agents. In the case of immune disorders, the immune system gets stuck in high gear, and inflammation does not recede. This is known as chronic inflammation.

Inflammation in the brain doesn’t look like it does in your body. Your brain doesn’t get visibly hot, red, and swollen. Inflammation in the brain means that microglia secrete excess inflammatory chemicals, called cytokines, that cause damage to needed neural structures or engulf and eliminate vital synapses. Just like white blood cells gather and inflame an area of the body, microglia can congregate in one area of the brain and do damage. This is referred to as neuroinflammation or, as in the case of some diseases like Parkinson’s and Alzheimer’s, neurodegeneration.

Erasing the Line Between Physical and Mental Health

Statistically, we’ve known that autoimmune diseases are more common in people (and their immediate families) with mood or cognitive disorders. We also know that adverse childhood experiences and other conditions creating chronic stress greatly increase a person’s chances of developing mental and physical diseases. Now we know why. Scientists used to assume that it was strictly a genetic link. While genetics does play a part and can predispose a person to susceptibility, we now know that environment (stress) and the immune system are also factors.

This means that the formerly imposed separation of physical and mental health simply does not exist. When a person’s immune system is overtaxed, the disease may show up in the brain or the body — or both. In the brain, microglia cells can do damage that set diseases in motion. Scientists have determined microglial dysfunction is associated with many neuropsychiatric diseases, including autism, Tourette’s, OCD, anxiety depression, schizophrenia, bipolar, and addiction. Nakazawa writes in The Angel and the Assasin:

All the big, bad, and difficult to treat brain-related diseases of our century, all of which are on the rise, share one common denominator: Immune-triggered microglia are wreaking havoc on the brain — very often in response to the same things that cause inflammation in the body.”

Neuroimmunology

Researchers call this new field neuroimmunology. Neuroimmunology bridges the gap between the mental and physical and forces us to look at the brain differently. There is no divide between physical health and mental health anymore. It is all connected, and it’s all health. Hopefully, new treatments, focusing on the body’s immune system and the brain’s microglia, will follow. The lag time between where science is and where patients are can be decades though, unfortunately.

Source: Nakazawa, Donna Jackson, The Angel and the Assasin, New York, NY, Ballantine Books, 2020.