Exploring the immune-brain conversation

Have you heard of the expression ‘healthy body healthy mind’? Well, it also works in the other direction healthy mind healthy body.

Up until a few decades ago, it was thought that the brain and the immune system existed as separate entities, but we now know nothing could be further from the truth. There are many ways the immune system signals the brain including the blood nervous system and blood-brain barrier transport mechanisms. We even have resident immune cells in the brain capable of immune signalling.


Why does the immune system communicate with the brain?


Immune-signalling molecules are involved in regulating many aspects of brain function. Importantly, when you have an infection like the flu, the brain needs to know you are sick so that it can induce a fever to help fight off the infection and also direct your behaviour.

So, when you are unwell you feel tired, down, lose your appetite and decide not to go to work, these behaviours are not accidental. They exist because the immune system has signalled the brain to cause these behaviours, which help you rest and recover to limit the impact of the illness.
However, there are times when the immune system can hijack the brain and cause long-term mental health issues such as depression, anxiety and reduce your cognitive ability. This can happen when inflammation becomes chronic or is very high. This causes a switch in the brain where someone can transition from these adaptive sickness behaviours into chronic depression, even if the initiating disease and inflammation have subsided.

Dr Adam Walker, Director of NeuRA’s Laboratory of Immunopsychiatry, is trying to identify what causes this transition and determine how we may be able to prevent and treat inflammation-induced psychiatric illness.
Immune-brain communication is bidirectional. That means the brain can talk back to the immune system. We have all heard how stress can cause you to feel run down and even more likely to get sick. One way this can happen is by suppression of the immune system from chronic stress.

We have two major stress systems in our body: the sympathetic nervous system, our fight or flight response, and the hypothalamic pituitary adrenal axis (HPA axis), our energy mobilisation response. Research shows that these stress response pathways modulate immune function and can suppress immunity, making you more vulnerable and make you respond worse to disease. It can even increase inflammation. There is growing evidence that nerves talk to immune cells which have been laid down for adaptive reasons, but with chronic psychological stress and continued activation of neural pathways the brain can subvert the immune system and impair its function.

NeuRA is trying to identify how to target the brain-to-immune signalling to improve health and wellbeing. This communication plays a pivotal role in daily life.


Chronic stress at work


A common source of chronic stress is our work life, where we are expected to meet constant deadlines, work long hours and deal with difficult situations. Imagine a scenario where chronic stress at work, and therefore chronic overactivation of your sympathetic stress response and HPA axis, induces inflammation and impairs immunity. The inflammation caused by stress elevates inflammation in the brain and impedes its optimal function. This, in turn, makes the brain less resilient against the stress of yet another deadline, which feeds back to your immune system and suppresses it further. That’s when you catch a cold from a colleague.

Your colleague only felt run down and had a runny nose for a day, but you just can’t seem to shake this off over the next couple of weeks. You end up needing to take a week off work. This cycle continues until you discover that you are really feeling down all the time. You do not interact with your friends and family and are really depressed.

Your depression makes you less productive at work and your performance is really lacking and you find yourself getting many more colds and being sick much more than you used to and having many more sick days.

Of course, most people, who get the flu do not become depressed and being stressed does not always lead to poor immune health.


Good news


The good news is that you can promote healthy psychological and physical wellbeing at home and in the workplace by managing stress, exercise, getting good quality sleep and many other ways that reduce the burden of your job on your body and your mind.

There are even ways your workplace can help improve your coping strategies and provide you with support, which will help maintain your cognitive function, reduce your fatigue and enhance your productivity at work.

For those individuals that are unlucky enough to develop inflammation-induced depression, Dr Walker is determining whether available drugs may be repurposed or new drugs designed that can treat this disorder.


Find out more

  • Discover more tips on improving mental wellness at work with NeuRA’s free eBook, available for download at NeuRAtalks.org