Select Page

Neuroinflammation is a broad term that is characterized by an immune response in the central nervous system (CNS) – the brain and spinal cord.  This abnormal immune response is initiated by cues including infection, bacteria, brain injury, toxins and autoimmunity.  Neuroinflammation is not a disease in and of itself but is a set of environmental conditions that has the potential to cause “malfunctions” in the brain and spinal cord.

In this article we will review the functions of the immune system, inflammation, and finally neuroinflammation.

What is inflammation?

Inflammation is the body’s natural response to injuries and infections. There are two types of inflammation, acute inflammation and chronic inflammation.

Acute inflammation is the body’s immediate response to an infection (a foreign and potentially dangerous invader). An injury or infection triggers the release of chemicals called inflammatory cytokines. These inflammatory cytokines activate the immune system to release immune cells that will come to the site of the infection, destroy and safely remove the infection, clean up any “debris” and leave the area. However, sometimes these immune cells do not leave the area. This is called chronic inflammation.

Chronic inflammation is when immune cells stick around too long and now instead of destroying a foreign invader, they start to destroy healthy tissue. This causes further release of inflammatory cytokines, causing the immune system to deploy more immune cells and a vicious cycle of cell death occurs.

If this occurs in the blood vessels, it causes damage to the blood vessel walls and results in atherosclerosis.

Chronic inflammation in the lungs will result in COPD, emphysema, asthma..etc.

If this occurs in the stomach it can lead to chrone’s disease, irritable bowel syndrome, leaky gut syndrome..etc.

And if this occurs in the brain and/or spinal cord it can contribute to Alzheimers disease, Parkinson’s disease, Psychiatric disorders, depression, anxiety…etc.

Before we move on to neuroinflammation, there is a little more detail about the immune system that is beneficial.

Inflammation and the immune system

The immune system is the body’s defense against infections, bacteria, and disease. It is not just one process, but a network of overlapping and interconnected processes. It is designed to differentiate healthy tissue from a foreign invader (bacteria, parasites, cancer, a wood splinter..etc) , encapsulate the foreign invader and remove it from the body. The immune system has two components, the innate immune system and the adaptive immune system.

What is the innate immune system?

The innate immune system is the first line of defense. When an injury occurs or a foreign invader enters the system the pro inflammatory molecules are released from the site of injury/foreign invader. This activates the immune system to deploy immune cells to the area there they will encapsulate the foreign material, and safely destroy it. The innate immune system is mainly a generalist and works well for common, broad categories of pathogens.  Once this step is complete, the clean up crew comes in and removes debris and the immune cells leave the area. In addition, these innate immune cells will take a piece of that foreign material back to the immune system’s home base (lymph nodes). This step helps the immune system learn about the invader should it ever return.

What is the adaptive immune system?

If the innate immune system fails and the foreign invader remains, the special operations team is deployed. This is called the adaptive immune system which contains antibodies for specific antigens that might escape the innate immune system.  Antibodies are “Y” shaped proteins that identify and attach to specific foreign invaders and neutralize them. Antibodies can stay in the body for a long time to offer long term protection.

This special ops team consists of B and T lymphocytes found in the tissue between the cells of the body.

T lymphocytes (T-cells) includes cells that release chemicals to attract other immune cells to come to the area (T-helper cells). There are also T cells that detect and foreign invader and destroy it (cytotoxic T cells).

T cells attach to foreign invaders like a lock and key. Each T cells fits into a specific lock. That means each foreign invader must be destroyed by a specific T cell. Once the T cells locks on, it can then multiply and produce more T cells with the same key to destroy more of that particular invader.

B cells are produced in the bone marrow and are activated by T cells. A B cell must contain the same “key” as the T cell. Meaning that each foreign invader has one specific B and T cell. Once the B cells is activated, it releases a specific antibody for that specific foreign invader (ie: virus, or bacteria). Antibodies attach to the foreign invader and destroy it. Bacteria and viruses that provoke the creation of antibodies are called antigens.

The brain’s own immune system

The central nervous system (brain and spinal cord) contains its own resident immune cells called microglia.  Microglia are activated by infections, bacteria, toxins, or autoimmunity. It is important to note that peripheral immune cells (immune cells in the body) are blocked from entering the brain by the blood brain barrier (BBB). The blood brain barrier is a filter that protects potentially damaging molecules from entering the brain.

What is neuroinflammation?

However, in some instances, the peripheral immune cells sneak past the blood brain barrier and enter the brain leading to neuroinflammation.  Neuroinflammation is not a “disease” in and of itself, but creates an environment in the brain in which diseases can flourish.  When immune cells from the body’s immune system get into the brain, it triggers the glial cells (brains own immune system) to deploy the brain’s immune cells (resident immune cells). The increase in activated immune cells cause further degradation of the blood brain barrier allowing potentially more peripheral immune cells into the brain and a viscous cycle ensues.

How does neuroinflammation impact the brain?

As stated earlier, neuroinflammation activates a bunch of peripheral and resident immune cells.  Immune cells release a free radical called reactive oxygen species (ROS). An excess amount of ROS causes oxidative stress. Oxidative stress has been linked to almost every non-communicable neurologic disease.