Inflammation Keeps Us Alive. It’s Also Making Us Sick. – The New York Times

Another obstacle, until recently, was a longstanding belief that the immune systems of the brain and body were separate. Anatomically speaking, there didn’t appear to be any lymph vessels in the brain to allow communication with the immune system.

Then, in 2015, Jonathan Kipnis and his colleagues found a network of tubes hidden in the meninges, the layers of membranes that surround the brain and spinal cord, linking them to the lymph nodes in the neck. The presence of these tubes overturned the assumption that the brain had its own self-contained immune system.

“There’s a lot of cross talk that’s going on between the whole body and the brain,” Beth Stevens, a neuroscientist who directs labs at Boston Children’s Hospital and the Broad Institute of M.I.T. and Harvard, told me. “I think with aging it becomes even more apparent, because when the body’s immune system is starting to become more inflammatory, that can affect the brain and maybe even vice versa.”

A little over a decade ago, Stevens made a discovery that changed what we know about immune-cell activity in the brain. She saw that macrophages exclusive to the central nervous system called microglia do more than clear away waste and damage; they also prune nerve cells that other immune proteins tag for removal during brain development so that synaptic connections are as efficient as possible. This synapse sculpting, which continues throughout our lives, raises the possibility that the immune system — if it malfunctions and trims the wrong cells — could be a driver of neurological disorders like schizophrenia as well as degenerative diseases like Alzheimer’s and Parkinson’s.

Stevens and her colleagues are trying to find ways to detect how the behavior of microglia and other immune cells changes when a healthy brain first begins to decline. That could give them a way to detect those diseases before a person develops symptoms by testing their blood or spinal fluid. “I don’t think it’s so crazy to think we might have that in the next few years,” Stevens says. That would in turn offer more options for developing ways to prevent and treat cognitive decline.

— Read on www.nytimes.com/interactive/2026/07/29/magazine/inflammation-chronic-immune-system-health.html