And yet, for all these threats, the war metaphor is misleading, incomplete—even arguably dead wrong. Your immune system isn’t a war machine. It’s a peacekeeping force that more than anything else seeks to create harmony. The job of the immune system is to circulate through this wild party, keeping an eye out for troublemakers and then—this is key—tossing out bad guys while doing as little damage to other cells as possible. This is not just because we don’t want to hurt our own tissue. It is also because we need many of the alien organisms that live on and in us, including the billions of
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