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Need to Know: Why Is the Blood Brain Barrier Important?

Columnist Tamara Sellman explains how this protective capillary barrier relates to disease-modifying therapies for MS patients.

What is the blood-brain barrier?

The blood brain barrier (BBB) is a highly dense network of cells that form a protective capillary barrier, separating brain tissue and cells from blood vessels.

The BBB prevents specific kinds of substances from entering the brain, namely pathogens, toxins, and plasma components, which could be damaging to the central nervous system (CNS).

At the same time, the BBB is very discriminating in what it will allow into the CNS. Only very specific blood components that are friendly and in service to the brain — such as hormones, water, oxygen, glucose (blood sugar), and vital nutrients — are permitted.

MS researchers care about the serviceability of the BBB because, when it’s defective, breaches occur that allow damaging substances to infiltrate the brain, leading to disease activity.


The capillaries that make up the BBB are similar to other blood vessels, composed of specific kinds of cells known as endothelial cells.

In other parts of the body, endothelial cells are somewhat porous, allowing substances to move through their membranes as required for proper function.

In the BBB, however, this capillary network is tightly constructed, only allowing for the passage of very small or specific kinds of molecules that serve the brain’s needs. This exchange is strictly regulated by special cells known as glial cells.

In the case of MS, the BBB experiences a breach by immune system cells (such as lymphocytes, or T-cells), which the glial cells cannot contain.

Situations that can lead to damage to the BBB include inflammation, disease activity, drug use, pollutants and toxins, smoking, or chronic oxidative stress.

Some specialists believe there’s also a possible connection between the health of the BBB and the health of the gut (the microbiome).

Read on: Need to Know: Why Is the Blood Brain Barrier Important?

The health and medical information on our website is not intended to take the place of advice or treatment from health care professionals. It is also not intended to substitute for the users’ relationships with their own health care/pharmaceutical providers.

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