Sympathetic Nervous System Research Paper

Sympathetic nervous system (SNS) stress responses accelerate our heart rate, constricts blood vessels, raises blood pressure to keep us ready for tense situations. Have you ever thought how stressful situations may affect your immune system? I will be breaking down a study that discusses a lesser-known effect of stress on our body, its effect on immune cells. This study outlines how stress can affect our immune cells, and its effect on immune responses. 

The sympathetic nervous system and its response to stress

When we encounter stressful situations, our body goes into a mode of “fight or flight.” The SNS is connected to a diverse number of biological systems, which results in many different effects in the body. Nervous systems rely on neurotransmitters to send signals across the body, and the main group of neurotransmitters for the SNS are catecholamines. 

The main catecholamines released in stress responses are adrenaline and noradrenaline. These two are responsible for the increased heart rate and sweaty palms in stressful situations! They can be thought of as a key to a lock. Keys need to have specific grooves on them to unlock the door they’re responsible for. In the SNS, the locks are also known as adrenergic receptors. The door that is unlocked is the stress response that we’ve all experienced.  

What do immune cells do?

Immune cells refer to the white blood cells that fight off infection in our body. When something foreign enters our body from the environment, they go through a series of interactions to coordinate an attack. There are many types of immune cells that have their own specific function, but the main ones for this study are T cells. 

T cells can be further differentiated into helper T cells and killer T cells. As their names suggest, helper T cells help organize the immune response by activating different types of immune cells. Killer T cells function to get rid of cells that are infected, “killing” them in the process.

How can stress affect immune cells? 

Immune cells are produced in the bone marrow then they travel through a system called the lymphatic system to lymph nodes. Here, they are stored for future use, and they can multiply when the time comes to fight infection. The SNS innervates lymph nodes, meaning – they are connected to lymph nodes. So, when the SNS responds to stress, noradrenaline can affect lymph nodes, affecting immune cells!

In this study, they experiment with noradrenaline and T cells by taking the lymph nodes of mice and added in noradrenaline. They observed the effects of the movement of T cells within the lymph nodes. Normally, immune cells would have some movement in the lymph nodes ready to fight off infection. However, upon addition of noradrenaline, this completely halted the movement of all T cells. 

This observation prompted the team to experiment with the “lock” of the response, the adrenergic receptor. So, instead of just adding in the same noradrenaline into mice, they added in another catecholamine into the mice. The same result was observed, all T cell motility was halted. The team came to the observation that when catecholamines (key) bind to adrenergic receptors (lock), T cell motility stops (door opens). 

What’s the purpose of this study?

In stressful situations, we expect the body to prepare for action. That’s why the palms get sweaty, and our heart rate increases. It may be expected to be the same for our immune system to be prepared for more movement of T cells, but the opposite was observed. When we are faced with stress, our T cells are completely paralyzed, not ready to identify and fight off infection.