CELLS that refuse to die could be the undoing of the immune system as we
age.
Immune T cells that carry proteins called CD4 and CD28 on their surface play
a crucial role in rallying immunity to an invading pathogen. But during normal
ageing, and in certain inflammatory diseases such as rheumatoid arthritis, half
the circulating T cells that carry CD4 can lose their CD28. These cells seem to
be less effective at boosting immunity and also develop dangerous tendencies,
such as killing other human cells.
It hasn鈥檛 been clear why these cells end up playing such a major role. Now
immunologist Abbe Vallejo and his colleagues at the Mayo Clinic in Rochester,
Minnesota, have shown that they have an unusual lust for life. Ordinary CD4 CD28
T cells undergo programmed suicide after they have fulfilled their function.
鈥淚t鈥檚 part of their job,鈥� says Vallejo. 鈥淭hey die to leave room for the next
generation of cells.鈥�
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But cells that lack CD28 ignore protein signals that normally trigger
suicide, Vallejo鈥檚 team has found. The cells can establish lineages that persist
for 3 years instead of the usual 2 months.
