Siglec Expression in Microglia

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Human Uniqueness Compared to "Great Apes": 
Likely Difference
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Microglia are a minor population of nervous system cells that originate from blood monocytes, which settle down in the brain to becomes the "macrophages" of the central nervous system.  Similar to macrophages in other tissues, they defend against infection by engulf invading pathogens and reacting to inflammation.  However, they also have trophic functions in supporting cells of the neural lineages, and may be involved in overrreacting to some inflammatory conditions.  While most peripheral tissue macrophages express multiple signaling molecules called "Siglecs", microglia usually do not not, under normal conditions.  The exception appears to be Siglec-11 and Siglec-16, which are expressed in the microglia of human but not "great ape" microglia.  This difference is associated with a human-specific gene conversion that involved the SIGLEC16 and SIGLEC11 genes.


Timing of appearance of the difference in the Hominin Lineage as a defined date or a lineage separation event. The point in time associated with lineage separation events may change in the future as the scientific community agrees upon better time estimates. Lineage separation events are defined in 2017 as:

  • the Last Common Ancestor (LCA) of humans and old world monkeys was 25,000 - 30,000 thousand (25 - 30 million) years ago
  • the Last Common Ancestor (LCA) of humans and chimpanzees was 6,000 - 8,000 thousand (6 - 8 million) years ago
  • the emergence of the genus Homo was 2,000 thousand (2 million) years ago
  • the Last Common Ancestor (LCA) of humans and neanderthals was 500 thousand years ago
  • the common ancestor of modern humans was 100 - 300 thousand years ago

Definite Appearance: 
100 thousand years ago


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