“Junk” Cells Maintain the Brain

The most abundant immune cells in your brain are not the neurons, but microglia – spindly cells that were thought to be static and immobile, the smallest of the glia cells that were once considered mere scaffolding to support the more important gray matter (see 11/20/2001 and 01/29/2001 entries).  When two scientists recently applied the new technique of two-photon microscopy to a live healthy mammalian brain, however, they were stunned at what they saw the microglia doing… “a static state is hardly what was observed,” reported Science magazine.¹.  They were the most motile cells in the brain.
    The little cells were observed to act like well-trained, active patrolmen doing a vital job.  They extended probes into their environment to monitor the health of the brain, clean up debris and fight microbes.  A caption explained:

Microglia continually extend … and retract … processes, surveying their immediate environment within the brain.  The processes move rapidly toward a site of injury, such as a damaged blood vessel in the brain, in response to the localized release of a chemoattractant … from the injured sited.  Once at the target site, the processes form a barrier to protect healthy tissue.   (Emphasis added in all quotes.)

Microglia comprise about 10% of cells in the central nervous system.  This monitoring and disaster response apparently goes on continually.  “These two elegant studies provide direct evidence for the highly dynamic nature of microglia, indicating that the brain is under constant immune surveillance by these cells.”  Who knows what we would think without them.

¹Luc Fetler and Sebastian Amigorena, “Brain Under Surveillance: The Microglia Patrol,” Science, Vol 309, Issue 5733, 392-393, 15 July 2005, [DOI: 10.1126/science.1114852].

Similar to the story on junk DNA (see 07/15/2005 entry), this goes to show that nothing in biology makes sense apart from design.  If we would approach biology with a design perspective (see 06/25/2005 entry), we might really begin to understand what life is all about.