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How Your Immune System Helps Direct Your Social Interactions

Story at-a-glance -

  • Your brain, immune system and gut microbes are intricately linked, affecting each other in surprising ways
  • Research suggests the immune molecule interferon gamma — a cytokine produced by your immune system in response to pathogens — may also play an important role in your social interactions
  • By blocking interferon gamma in the brain of a mouse, researchers were able to induce hyperactivity and abnormal behavior. When they restored the molecule, both problems disappeared

By Dr. Mercola

That your immune system is your first line of defense against disease is nothing new. Interestingly, recent research suggests your immune system may also play a role in your social interactions.1 In fact, researchers now believe your immune system may actually be a controlling factor in your behavior.

In the referenced study, by blocking a specific immune molecule in the brain of a mouse, the mouse brain displayed hyperactivity, resulting in abnormal, asocial behavior. When they restored the molecule, both problems disappeared.

Is Your Personality Dictated by Your Immune System?

Scientists believe this discovery may have "enormous implications for neurological conditions such as autism and schizophrenia."2

According to Jonathan Kipnis, Ph.D., chairman of the Department of Neuroscience and director of the Center for Brain Immunology at the University of Virginia (UVA) School of Medicine:

"The brain and the adaptive immune system were thought to be isolated from each other, and any immune activity in the brain was perceived as sign of a pathology.

And now, not only are we showing that they are closely interacting, but some of our behavior traits might have evolved because of our immune response to pathogens.

It's crazy, but maybe we are just multicellular battlefields for two ancient forces: pathogens and the immune system. Part of our personality may actually be dictated by the immune system."

Your Brain, Gut and Immune System Are All Linked

Kipnis was part of the team that, just last year, discovered there's a direct link between the brain and immune system.

Similar to blood vessels that carry blood throughout your body, previously unknown lymphatic vessels carry immune cells throughout your body, including your brain, which was previously thought to be impossible.

It's becoming increasingly clear that your brain, immune system and your gut microbes are intricately linked, affecting each other in surprising ways. Autism, for instance, is associated with gastrointestinal problems and, potentially, an over-reaction in the immune system.

Neurological diseases like multiple sclerosis (MS) and Alzheimer's have also been linked to immune dysfunction, and autoimmune diseases such as Crohn's disease share certain traits with psychiatric illness.

It wasn't always clear how such connections occurred, but now scientists have uncovered three important and interconnected pieces:

The gut-brain axis (in recent research, scientists were even able to raise or lower blood sugar and insulin, and increase or suppress hunger, simply by activating and deactivating certain neurons3)

The pathway between your immune system and your brain

The influence of your immune system on your brain and behavior

In addition to that, we now know your microbiome also helps control gene expression, so by optimizing your gut flora, you are actually influencing your genes in a positive way.

How Interferon Gamma Influences Your Brain and Behavior

Getting back to the featured study, the UVA reports that:4

"The relationship between people and pathogens … could have directly affected the development of our social behavior, allowing us to engage in the social interactions necessary for the survival of the species while developing ways for our immune systems to protect us from the diseases that accompany those interactions.

Social behavior is, of course, in the interest of pathogens, as it allows them to spread."

The immune molecule identified as a "critical" player in social behavior is known as interferon gamma (G), a cytokine normally produced by your immune system in response to pathogens such as viruses, bacteria and parasites. In your brain, interferon G inhibits neurons in your prefrontal cortex.

This is normal and healthy. Without interferon G suppressing these neurons, your prefrontal cortex can go into overdrive, as it did in the mice in this study. When the researchers blocked interferon G in their brains, the mice became hyperactive and less social.

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Social Interactions and Spread of Pathogens

As for why the same molecule responsible for normal social behavior would also be triggered by pathogens — which suggests that pathogens would be more easily spread between people — the researchers can only speculate. As reported by The Atlantic:5

"'We were really fascinated by why this antipathogen molecule would have a prosocial function — that doesn't really make sense,' says Anthony Filiano, [Ph.D.]… lead author on the study

… [G]athering in groups makes diseases more likely to spread. Why, evolutionarily speaking, is that something the immune system would want to promote? ...

'Naturally if individuals tend to spread diseases, that could easily result in extinction of the whole colony,' [co-author Vladimir] Litvak [Ph.D.] says. 'So you have to have a very strong immune response.'

Maybe the immune system activates when animals are socializing to protect them against the increased risk of getting a disease."

While entirely speculative, I'd propose another potential mechanism. Your body contains 10 times more bacteria than it does cells, plus viruses, which in turn outnumber the bacteria 10 to 1.

You are in a sense a walking, talking mass of microorganisms, and these organisms are involved in a wide range of biological and biochemical regulatory functions.

It has previously been suggested that human evolution may in part have been driven by the introduction of new pathogens (and/or beneficial microorganisms) into our system,6,7,8 and this research appears to support the idea that we may be "programmed" to share pathogens with others in our group to spread immunity.

So rather than outright defending against disease, it may be that by sharing disease the people in the group and subsequent generations build stronger immunity or immune system defenses and/or incorporate new, important microbes into our biology.

The Importance of a Healthy Gut Microbiome

As mentioned, the microorganisms residing in your gut — collectively known as your gut microbiome — preside over a wide array of biological functions and are closely interconnected with both your brain and your immune system. For example, researchers at the University of California, Los Angeles (UCLA) found they could alter the brain function and mood of participants in a beneficial way by giving them probiotics (healthy bacteria).9

Gut bacteria also influence your immune function. Biologist Sarkis Mazmanian, Ph.D.,10 believes bacteria can actually train your immune system to distinguish between "foreign" microbes and those originating in your body. His work is laying the groundwork for new therapies using probiotics to treat a variety of diseases, particularly autoimmune diseases such as MS and Alzheimer's.

Researchers have also discovered that the absence or presence of gut microorganisms during infancy permanently alters gene expression.11 Through gene profiling, they've been able to discern that absence of gut bacteria in mice altered genes and signaling pathways involved in learning, memory and motor control.

This suggests gut bacteria are closely tied to early brain development and subsequent behavior. These behavioral changes could be reversed as long as the mice were exposed to normal microorganisms early in life. But once the germ-free mice had reached adulthood, colonizing them with bacteria did not influence their behavior.

Gut Bacteria and Chronic Fatigue Syndrome

Recent research suggests gut bacteria may also play an important role when it comes to addressing chronic fatigue syndrome (CFS). According to Maureen Hanson, Ph.D., senior author of the study in question, CFS patients have "a different profile of bacterial species in their gut microbiome than healthy individuals."12

Not surprisingly, CFS patients as a rule had more species of bacteria known to promote inflammation, and fewer of those that help combat inflammation. Those with CFS also had less diversity of bacteria than healthy subjects.

That said, not all CFS patients had radically abnormal microbiomes. Some were "fairly normal," yet still struggled with symptoms of CFS. So while gut flora appears to be part of the dysfunction, it's unlikely to be the sole cause. Aside from hinting at potential treatments using probiotics, which have yet to be investigated, this research also suggests you may be able to use microbiome testing as a diagnostic tool. As reported by

"Using the microbiome findings, the researchers said they were able to correctly classify whether 83 percent of the study volunteers had [CFS] or didn't. If these findings are confirmed in a larger study, the authors suggested that the gut microbiome could be used as an additional test to determine if it's likely that someone has [CFS]."

How to Optimize Your Gut Flora

Considering the fact that an estimated 80 percent of your immune system is located in your gut, nourishing your gut and regularly reseeding it with healthy bacteria is important for the prevention of virtually ALL disease, from colds to cancer. To do so, I recommend the following strategies:

Eat real food and avoid processed, refined foods in your diet. It is especially important to avoid all sugars and grains and keep your net carbs (total carbs minus fiber) to under 50 grams per day. You can use to help you monitor this.

Eat traditionally fermented, unpasteurized foods: Fermented foods are the best route to optimal digestive health, as long as you eat the traditionally made, unpasteurized versions. Some of the beneficial bacteria found in fermented foods are also excellent chelators of heavy metals and pesticides, which will also have a beneficial health effect by reducing your toxic load. Healthy choices include:

Fermented vegetables of all kinds (cabbage, carrots, kale, collards and celery spiced with herbs like ginger and garlic)

Lassi (an Indian yogurt drink)

Fermented raw milk such as kefir or yogurt, but NOT commercial versions, which typically do not have live cultures and are loaded with sugars that feed pathogenic bacteria

Natto (fermented soy)


Ideally, you want to eat a variety of fermented foods to maximize the variety of bacteria you're consuming. Fermented vegetables, which are easy and economical to make at home, are an excellent way to supply beneficial bacteria back into our gut.

As an added bonus, they can also be a great source of vitamin K2, provided you ferment your own using the proper starter culture. We tested samples of high-quality fermented organic vegetables made with our specific starter culture, and a typical serving (about 2 to 3 ounces) contained 10 trillion beneficial bacteria and 500 mcg of vitamin K2, which is an important co-nutrient to both vitamin D and calcium.

Take a high-quality probiotic supplement if you don't eat fermented foods on a regular basis.