Their natural killer cell numbers, for instance, have normalized and a few have largely recovered.

FORBES: Connect

Natural killer cells normally play an important role in inducing apoptosis of cancerous cells and others that have been infected with viruses.

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Two specific types of immune system cell that attack invaders - CD4 T-cells and natural killer cells - increased in number with age, with a higher rate of increase in women than in men.

BBC: Biological clue to why women live longer than men

Natural Born Killer star Juliette Lewis.

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Scotts plans to gradually introduce more gardening soil, fertilizer and bug killer made with natural ingredients, including animal manure and Sri Lankan coconut husks.

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Chocolate is a natural analgesic, or pain killer.

CNN: Researchers say chocolate triggers feel-good chemicals