How does the brain's immune system work?

The brain's immune system is complex and involves specialized cells known as microglia. Microglia are derived from the same stem cells as other immune cells in the body, such as macrophages and monocytes. These cells not only provide architectural support in the brain but also play a critical role in communication and immune response 1.

Microglia are the brain's primary immune cells and act as its surveillance and defense system. They identify threats like infections or damaged cells and shift between a resting state and an activated, inflammatory state in response to these threats. This mechanism is crucial for protecting the brain from various pathogens and maintaining cellular health 2.

In the event of an immune response triggered elsewhere in the body, inflammatory markers can cross the blood-brain barrier and activate these microglial cells. Additionally, certain regions of the brain have more permeable barriers, allowing immune markers to penetrate and influence brain function through the vagus nerve and other pathways 2.

Moreover, the brain's immune system is intricately connected to the gut, forming a complex communication network known as the gut-brain axis. This network allows the gut's immune responses to send signals to the brain, impacting processes related to neuroinflammation and cognitive function 1 3.

Ultimately, while microglia play a protective role, chronic overactivation can lead to persistent inflammation, contributing to neurodegenerative diseases like Alzheimer's and Parkinson's, as well as mood disorders 2. This highlights the critical balance required for maintaining brain health and preventing cognitive decline.