Thursday, 19 January 2012

Parasitic Worms and Wound Healing

Parasites can do you good. I didn’t discuss it at length in Parasites: Tales of Humanity’s Most Unwelcome Guests (I touched on it in chapter six), but I’m fascinated by the growing evidence that at least some of our parasites have good things to contribute to our health. The latest piece of that puzzle is research showing that hookworms can initiate an immune response in the host that actually speeds healing of tissue damage.

The business end of a hookworm.
You may not like the idea of hosting a few
hookworms, but they might return the favor
with better health. CDC; CC BY-SA 3.0

In their paper “An essential role for TH2-type responses in limiting acute tissue damage during experimental helminth infection,” Fei Chen et al report that in mice “IL-17 initially contributed to inflammation and lung damage, whereas subsequent IL-4 receptor (IL-4R) signaling reduced elevations in IL-17 mRNA levels, enhanced the expression of insulin-like growth factor 1 (IGF-1) and IL-10 and stimulated the development of M2 macrophages, all of which contributed” to healing (Nature Medicine, published online 15 January 2012). In other words, there was an inflammatory response to the worms at first, then inflammation was suppressed while healing was enhanced.

It’s reasonable that a healing response may have evolved to help the host’s body deal with damage done by the worms themselves, but of course the potential exists for us to use that response to help heal tissue damage from other causes. This new report also ties in with previous work that suggests the ability of some of our parasites to suppress inflammation may protect us from autoimmune diseases.

It does make sense to me that organisms that have been with us for millions of years would have a relationship of both give and take with the host. While it’s true that parasitic diseases are some of the worst we face, and hookworm is a nasty parasite, I think we need to set aside the idea that anything parasitic is utterly bad. Let’s get to know them properly before we send them to extinction. (Not that hookworm is in danger of going extinct any time soon.)

I think we still have a lot to learn about our relationship with our parasites, especially our "old friends."

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