Eosinophils in the gastrointestinal tract : friends or foes ?

Eosinophils play an important role in the mucosal immune sys- tem of the gastrointestinal tract under resting and under inflam- matory conditions. Under steady-state conditions, the mucosa of the digestive tract is the only organ harboring a substantial number of eosinophils, which, if need be, get activated and exert several effector and immunoregulatory functions. The precise function of these late- phase inflammatory cells is not yet completely understood. Nevertheless, it has recently been demonstrated that lipopolysac- charides from gram-negative bacteria activate eosinophils to rap- idly release mitochondrial DNA in the extracellular space. Released mitochondrial DNA and eosinophil granule proteins form extracellular structures able to bind and inactivate bacteria. These findings suggest a novel mechanism of eosinophil-mediated innate immune responses that might be important in maintaining the intestinal barrier function.