AILSA CHANG, HOST:
Japan has one of the highest concentrations of supercentenarians in the world. That's people who live to be at least a 110 years old. Now, researchers there are studying their immune systems for clues on their remarkable longevity. NPR's Pien Huang has more.
PIEN HUANG, BYLINE: Kosuke Hashimoto at the University of Osaka says there are about 150 or so of these so-called supercentenarians spread throughout Japan.
KOSUKE HASHIMOTO: So they have to find everywhere from Hokkaido to Kyushu, south to north.
HUANG: They're not easy to find, but for researchers looking into how people stay healthy as they age, tracking them down is worth it.
HASHIMOTO: Those people tend to have less cancer or heart disease, so their immune systems still function very well.
HUANG: Hashimoto and his colleagues looked at immune cells from blood samples from 10 of them. Compared with younger adults - that's relatively younger, those over 70 - the supercentenarians had a much higher ratio of a specific type of immune cell, one that's also found in the bodies of people fighting certain cancers. Now, these super agers showed no signs of those cancers, but Hashimoto says aging bodies are known for making abnormal cells and proteins that can lead to cancer.
HASHIMOTO: It is clear that more mutation happens. Those are like new adaptation in the late phase of aging.
HUANG: In their new paper, published in Cell Reports, Hashimoto and his colleagues think they're seeing a new stage in immune development that kicks in around age 100, that of the immune system adapting to a new priority, tackling abnormal cells in aging bodies. That's the theory, at least. David Masopust at the University of Minnesota researches human immune systems.
DAVID MASOPUST: It's a great hypothesis. It would demand a lot of further work. It will be very hard to untangle the correlation with any kind of causation.
HUANG: Masopust says there are several well-documented stages of immune development, starting as an infant.
MASOPUST: So when we're young, you know, you go to daycare and it's the dirtiest place in the world, and you, you know, have a pretty lousy immunity to most things.
HUANG: There are changes in the teen years, midlife and later years, all thought to help the body adapt to what it's likely to encounter in those stages. But Masopust says, by age 100, it's not clear if changes to the immune system are doing anything helpful or just happening.
MASOPUST: I just don't think there's a ton of selection pressure to get 110-year-old people to live one more year.
HUANG: Hashimoto, the study author, agrees that there are just limits to aging bodies, even those with super immune systems. The longest living person known to science died decades ago at 122 years old. No one has exceeded that since. Pien Huang, NPR News.
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