T cells start to lose their identities as they get older, recent Emory research indicates.
Immunologists Cornelia Weyand and Jorg Goronzy, who are codirectors of the Lowance Center for Human Immunology at Emory University School of Medicine, have a just-published paper in the journal Blood describing this phenomenon.
Weyand and Goronzy show that with age, T cells begin to turn on genes that are usually turned on only in â€œnatural killerâ€ cells. NK cells play a major role in rejecting tumors and killing cells infected by viruses. They are white blood cells like T cells but they have a different set of receptors on their surfaces controlling their activities.
Many of these receptors act to hold the NK cells back; so when they appear on the T cells, their activation is dampened too, thus contributing to the slowing down of the immune system in elderly people.
The authors report that NK cell genes get turned on because they lose the â€œmethylationâ€ on their DNA. Methylation is a pattern of tiny modifications on DNA, emphasizing whatâ€™s important (or forbidden) in a given cell, sort of like a highlighterâ€™s yellow pen on top of text.
Apparently, in elderly people (aged 70-85), the methylation is more â€œspottyâ€ than in younger people (aged 20-30). It seems that after the DNA is copied several times, the highlighting gets fuzzy and the T cells start to look like their cousins, natural killer cells.