JUST THE BASICS

The brain (in this cartoon, the treehouse) is considered a site of “relative immune privilege.” This means that, in most situations, the brain is largely sealed off from the rest of the immune system. The brain limits the entry of immune cells for good reason. A lot of immune reactions trigger swelling, which is very dangerous for the brain. With a bony skull surrounding it and little room to expand, brain swelling can lead to brain damage. That doesn’t mean the brain has no immune system, though! It has specialized cells called microglia that protect it without triggering a lot of inflammation, and it makes high levels of antiviral compounds.

TELL ME SOMETHING NERDY

TLR3 deficiency is a type of primary immune deficiency that leads to recurrent herpes simplex virus (HSV) encephalitis. Intriguingly, it doesn’t lead to an increase in infections outside of the brain. Why is that? TLR3 helps the brain make interferon beta, which is a critical part of the brain’s antiviral response to HSV. Without it, the brain’s ability to fight off HSV is impaired. Peripheral immune cells, on the other hand, have multiple mechanisms they can use to respond to HSV, and can recruit other cell types to help them fight off an infection in the rest of the body.

Published in November 2023 Annals of Allergy, Asthma & Immunology: https://doi.org/10.1016/j.anai.2023.06.010

Abbreviations: CNS - central nervous system; PBMCs - peripheral blood mononuclear cells; NK Cell - natural killer cell; HSV - herpes simplex virus; TLR3 - toll-like receptor 3