According to a study published in the journal Cell, cerebrospinal fluid (CSF), which circulates inside of and around the brain and spinal cord, provides immune protection to the brain. But this function has not been well studied.

A study of CSF revealed that the CSF immune system becomes dysregulated as people age. The study also revealed that in people with cognitive impairment, such as those with Alzheimer’s disease, the CSF immune system is drastically different from that of healthy individuals.

In the study, the researchers used a technique called single-cell RNA sequencing to analyze the CSF. Using this technique, they profiled 59 CSF immune systems across a spectrum of ages by taking CSF from participants’ spines and isolating their immune cells. In the first part of the study, they looked at CSF in 45 healthy individuals aged 54 to 83 years, while in the second part of the study, they compared those findings in the healthy group to CSF in 14 adults with cognitive impairment, as determined by their poor scores on memory tests.

The findings of the study showed that in the cognitively impaired group, inflamed T cells cloned themselves and flowed into the CSF and brain. They also found an overabundance of a cell receptor, CXCR6, in cells, which acts as an antenna. They observed that this receptor received a signal from another receptor, CXCL16, from the degenerating brain’s microglia cells to enter the brain. 

(Source: https://theprint.in/health/researchers-discover-immune-reservoir-to-treat-alzheimers-disease/1264590/ )