People past 110 carry an unusual immune profile in their blood. In that group, cytotoxic CD4 T cells accounted for a median of 17.6 percent of all T cells. Among 100- to 109-year-olds the share was 9.6 percent, among 70- to 99-year-olds 4.0 percent. A team at the University of Osaka led by Kosuke Hashimoto analysed blood samples from 28 adults. The results appeared in the journal Cell Reports on 19 August.
Ageing research treats the very old as a model of healthy ageing. They reach an extreme age and often stay free of cardiovascular disease and cancer for a long time. Why they manage that is unresolved. Immune defence normally weakens with age, while inflammation increases.
The cells now in question run against that pattern. Ordinary CD4 T cells direct other immune cells. The rare cytotoxic variants, known as CD4 CTLs, also attack on their own. They destroy infected, degenerate or aged body cells, the science magazine scinexx reports.
The team combined single-cell sequencing with an analysis of T cell receptors. The increase does not rest on many different cells. Instead, individual clones had multiplied strongly. The most common clone in each participant made up 33.3 percent of their CD4 CTLs on average. In one centenarian, a single clone accounted for 53.8 percent. Such expansions occur when the same target challenges the immune system over a long period.
Matches from a cancer database
The researchers compared the receptor sequences with a public database. Almost three dozen matches came from people with lung, breast or liver cancer, Medical Xpress reports. None of the very old participants had such a diagnosis. "These cells may help to detect tumours before they become clinically detectable," Hashimoto says, quoted by wissenschaft.de.
That is not proof. The study shows neither protection against cancer nor a contribution to longevity. It captured only T cells circulating in blood, not in tissue. Twenty-eight people are also a small group. Age alone does not decide the matter either: the highest share in the whole study belonged to a participant under 100.
"Immune aging is not simply a process of decline," Hashimoto says. The selective expansion of certain T cells suggests that the immune system still adapts in extreme old age. Next, the team plans to examine how these cells behave in human tissue.