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Your Immune System 'Remembers' Microbes It's Never Fought Before, New Study Says

Immune cells build up strength against common bugs we encounter everywhere, and this helps us resist more dangerous ones. Kids eating dirt: Maybe a good thing.
By Rebecca Boyle Posted 02.07.2013 at 4:01 pm

Immune cells are like the Hatfields and McCoys of our bodies--once wronged, they never, ever forget. This is how we gain immunity, and it’s why vaccines work: Immune cells develop a memory of an invading pathogen, and they build an alert system to find and fight it should it ever return. But a new study by Stanford researchers adds a new wrinkle to this long-held immune theory. It turns out immune cells can develop this memory-like state even for pathogens they’ve never met. This may come from exposure to harmless microbes -- or the memories may actually be borrowed from other, more experienced cells.

The findings could help explain why babies and small children are so susceptible to infectious diseases. They haven't been exposed to enough ever-present, mostly harmless pathogens yet, and it's the constant scuffle with these bugs that gives adult T cells a sort of cellular precognition. “It may even provide an evolutionary clue about why kids eat dirt,” said the study’s lead author, Stanford microbiologist and immunologist Mark Davis. Kids are drawn to dirt because they’ve got to expose their fledgling immune systems to something, to help build up their defenses.

Davis and his coauthors studied a group of T cells called CD4 cells, which are the same ones targeted by HIV. CD4 cells hang out in our bloodstreams and stand sentinel, sounding the cellular alarm when they spot something that doesn’t belong. There are two basic classes of CD4 cells: Naive cells, which haven’t been exposed to a particular bug and might take a while to mount a response, and memory-type cells, which have done battle with a pathogen and are on the lookout for it again. The memory cells can prompt action within a few hours, while naive cells might take days or even weeks--meanwhile, we’re sick.

read more http://www.popsci.com/science/article/2013-02/your-immune-sy...

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