T Cell Reactivity

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.