How does the blood-brain barrier help protect the nervous system from infection?

The blood-brain barrier serves as a critical defense mechanism for the nervous system by acting as a selective filter between the bloodstream and brain tissue.12

This barrier is created by the modification of brain capillaries, which feature reduced fenestration and tight cell-to-cell contacts. Additionally, glial cells wrap around these capillaries, requiring substances to diffuse through multiple layers to reach nerve cells. By maintaining these tight capillary walls, the barrier effectively prevents many harmful substances, including various microorganisms, from leaving the blood and entering the brain.321

While the barrier is highly effective at blocking large molecules and many water-soluble chemicals, it can be compromised by bacteria, viruses, and fungi. If the barrier sustains damage, the nervous system's resistance to infection decreases, potentially leading to serious inflammatory conditions such as meningitis or encephalitis.1