T Cell Reactivity

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Human Uniqueness Compared to "Great Apes": 
Likely Difference
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Human T cells were found to give much stronger proliferative responses to specific activation compared to those from chimpanzees.   Non-specific activation using the lectin phytohemagglutinin (PHA) was reasonably robust in chimpanzee T cells, indicating that there is no intrinsic inability to respond to an activating stimulus. One possible explanation is the human-specific loss of T cell expression of CD33-related Siglecs, which are inhibitory signaling molecules that are thought to downregulate cellular activation via cytosolic immunoreceptor tyrosine-based inhibitory motifs. Of note, humans seem more prone to diseases associated with excessive T cell activation, such as hyperimmune responses to viruses, bronchial asthma and rheumatoid arthritis.


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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