Saturday, April 16, 2016

Worm infection tips the balance in favor of Crohn's disease soothing gut flora

This week Science magazine published yet another study that revealed a complex biological inter-species relationship called defensive symbiosis. Here, the authors showed that worm infection of mammalian host favors gut flora species that soothe intestinal inflammation in a TH2-dependent manner.

Mice deficient in Nod2 develop small intestinal abnormalities that resemble human Crohn's disease (for example, goblet cell defect that compromises intestinal mucus layer). This new study showed that experimental infection of Nod2-deficient mice with the parasitic worm Trichuris muris (T. muris) could restore small intestinal goblet cell numbers and morphology.

Earlier reports showed that intestinal abnormalities in Nod2-deficient mice dependent on gut flora species, Bacteroides vulgatus. Now, the authors showed that T. muris worm infection could reduce Bacteroides vulgatus burden in Nod2-deficient mice in a manner dependent on STAT6 signaling and IL-13 (type II immunity). Similar results were seen with a second worm infection, Heligmosomoides polygyrus.

Finally, the authors showed that worm infection specifically expanded another gut flora species, Clostridiales, that could directly inhibit pro-inflammatory Bacteroides vulgatus.

In summary, this study showed that in Nod2-deficient mice gut species Clostridiales represent defensive symbionts with an antagonistic interaction with another commensal bacteria, Bacteroidales. Worm infection of Nod2-deficient mice tips the balance in favor anti-inflammatory Clostridiales species. This knowledge could be utilized in treatment of Crohn's disease (for example, therapeutic worm infection or application of its derivative that promote type II immunity). 

David Usharauli

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