White blood cell uses DNA protein traps to fight bacteria

August 14th, 2008 - 4:55 pm ICT by IANS  

Washington, Aug 14 (IANS) Scientists have discovered how eosinophil, a type of white blood cell, helps fight bacterial infections in the digestive tract. Hans-Uwe Simon of University of Bern, Switzerland, Gerald J. Gleich of University of Utah School of Medicine and colleagues discovered that the presence of bacteria activates eosinophils to release mitochondrial DNA in a catapult-like fashion to create a net that captures and kills them.

“This is a fascinating finding,” said Gleich, a dermatologist and a co-author of the study. “The DNA is released out of the cell in less than a second.”

Eosiniphils, which comprise only one to three percent of human white blood cells (WBCs), are frontline soldiers in the body’s defence against parasites. But their exact role in the immune system is not clear.

Unlike other WBCs, eosinophils are found only in selected areas like the digestive tract. Mitochondria - often referred to as the power plants of the cell - are components within cells descended from ancient bacteria. Although most cellular DNA is contained in the nucleus, mitochondria have their own DNA.

Previous research has shown that eosinophils secrete toxic granule proteins during parasite infections which finish off bacteria. Simon, Gleich and colleagues found that when eosinophils are stimulated by infection, such as E. coli, they rapidly secrete mitochondrial DNA.

This DNA binds to the granule proteins and forms a net that is able to trap and kill bacteria. The researchers also found higher levels of eosinophils were linked to improved survival and lower numbers of bacteria in the blood of mice with widespread bacterial infections.

But toxic proteins released by eosinophils can also damage nearby tissues. The inflammation in some types of asthma and Crohn’s disease, an inflammatory bowel disease, is attributed to eosinophils.

In fact, Simon and his team first found evidence of these DNA-protein traps in tissue taken from the digestive tracts of people with Crohn’s disease.

These findings have been published in this week’s online edition of Nature Medicine.

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