Neutrophils from hereditary hemochromatosis patients are protected from iron excess and are primed

Abstract

Iron is required for the oxidative response of neutrophils to allow the production of reactive oxygen species (ROS). However, neutrophil function may be severely altered in conditions of iron overload, as observed in chronically transfused patients. Therefore, a tight regulation of neutrophil iron homeostasis seems to be critical for avoiding iron toxicity. Hepcidin is the key iron regulator in organisms; however, no studies have investigated its role in maintaining neutrophil iron homeostasis or characterized neutrophil function in patients with hereditary hemochromatosis (HH), a common iron overload genetic disorder that results from a defect in hepcidin production. To explore these issues, we studied 2 mouse models of iron overload: an experimentally induced iron overload model (EIO), in which hepcidin is increased, and a genetic HH model of iron overload with a deletion of hepatic hepcidin. We found that iron-dependent increase of hepatic hepcidin results in neutrophil intracellular iron trapping and consecutive defects in oxidative burst activity. In contrast, in both HH mouse models and HH patients, the lack of hepcidin expression protects neutrophils from toxic iron accumulation. Moreover, systemic iron overload correlated with a surprising neutrophil priming and resulted in a more powerful oxidative burst. Indeed, important factors in neutrophil priming and activation, such as tumor necrosis factor α (TNF-α), VCAM-1, and ICAM-1 are increased in the plasma of HH patients and are associated with an increase in HH neutrophil phagocytosis capacity and a decrease in L-selectin surface expression. This is the first study to characterize neutrophil iron homeostasis and associated functions in patients with HH.