Don’t Look Now, But Your Immune System Kind of Wants to Kill You

Everyone wants a strong immune system. It’s one of many reasons people work out. It’s why people get flu shots. It’s why we eat fruits and vegetables and carrot juice and supplements. But it turns out a robust immune system isn’t always good for you.

Your Inner Jekyll and Hyde

Your immune system is made up of many components, but one of them is the macrophage: a versatile type of white blood cell, produced in your bone marrow, that disposes of dead tissue and fights disease by attacking microbes. Macrophages have been called the “garbage collector” and “housekeeper” of the human body — though in her book “Natural Causes: An Epidemic of Wellness, the Certainty of Dying, and Killing Ourselves to Live Longer,”Barbara Ehrenreich proposes the more respectful title of “all-purpose handyman.”

Macrophages deserve respect, Ehrenreich explains. They can do a lot to protect you, and they have a surprising amount of autonomy. They function much like lone amoebas — they can move around on their own, and they actually eat the dead cells they stumble upon, so they have a food source independent from the bloodstream.

Unfortunately, macrophages have so much autonomy, they can take a traitorous turn.

Scientists have long known that macrophages cluster around cancerous tumors. Around the turn of the 2000s, though, they realized that macrophages weren’t fighting the cancer or even being neutral — they were making things worse. They “excite” cancer cells, as Ehrenreich puts it.

In fact, macrophages are central to the way breast cancer and many other types of cancer metastasize. Once they pair up with a helpful macrophage, cancer cells that couldn’t migrate easily on their own get a free pass through the body. Which begs the question: Why is this element of our immune systems helping cancer, and not us?

Ban Macrophages?

It’s not that simple. Macrophages do good work in our bodies, too. They protect us from harmful microbes that can cause a wide range of diseases, from strep throat to AIDS. Under the right circumstances, they can even protect us from cancer — their favorite disease!

See, researchers have found that many cancerous cells sneak through the body unnoticed because they have a surface molecule, CD47, that functions as a “healthy cell, don’t eat me!” signal. Macrophages are totally bamboozled by this trick. When they’re confronted by cancer cells un-disguised in CD47, though, macrophages fly into action and absolutely obliterate them. As a result, one topic of current cancer research is how to keep cancer cells from producing CD47.

So what does this mean about macrophages? For some scientists, it’s proof that they’re incredibly flexible. They’re like people, in a way — capable of great good (strengthening the immune system) and great evil (helping cancer metastasize). Some researchers are working on ways to teach the cells not to kill us through assorted stimulations and therapies. This is commonly called “macrophage re-education.”

For Ehrenreich, though, macrophages’ two-faced nature means something different: that they might be total free agents, “doing what they feel like doing” with little interest in the health of our bodies overall. Perhaps, she argues, our idea of the body as a harmonious whole is a pleasant fiction. Really, just as we sometimes feel conflicted, our bodies are sometimes physically conflicted. Cells war against other cells. Sickness isn’t necessarily a sign that something is “wrong” — it can be seen simply as a symptom of the constant, microscopic turmoils within us.

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