An Entrapment Defense

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Science  22 Aug 2008:
Vol. 321, Issue 5892, pp. 1021
DOI: 10.1126/science.321.5892.1021b

Eosinophils are white blood cells that play a critical role in protecting vertebrates from parasitic infections and also are believed to participate more broadly in immune defense. Yousefi et al. suggest that eosinophils serve to protect the gastrointestinal tract from unwanted bacterial invaders, and they do so by engaging an unusual mechanism. Analyzing colon tissue from patients with Crohn's disease (a chronic intestinal inflammatory disorder), they found that a subset of the infiltrated eosinophils were associated with extracellular structures that contained DNA and eosinophil-derived granule proteins. In vitro studies revealed that when treated with lipopolysaccharide from bacterial pathogens, eosinophils released their mitochondrial DNA in an explosive fashion. This DNA release was dependent on priming of the cells with cytokines and resulted in rapid death of co-cultured bacteria, although the eosinophils themselves remained viable. Mice that had been manipulated genetically to overproduce eosinophils displayed similar extracellular structures in their intestine in response to surgically induced sepsis, and they survived longer than control mice. Thus, these eosinophil-derived structures appear to trap and kill bacterial invaders in the gut. Other researchers had shown previously that neutrophils and mast cells also produce extracellular traps with antimicrobial activity, but in those instances the expelled DNA was nuclear rather than mitochondrial, and that strategy resulted in the death of the immune cells. — PAK

Nat. Med. 14, 10.1038/nm.1855 (2008).

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