Norepinephrine-Mediated Suppression of Phagocytosis by Wound Neutrophils 1

BackgroundThe systemic response to injury is characterized by massive release of norepinephrine (NE) into the circulation as a result of global sympathetic activation. Multiple authors have demonstrated NE-mediated alterations in migration of circulating neutrophils to wounds. We hypothesized that NE further alters wound neutrophil phagocytic function through adrenergic signaling pathways.MethodsA standard subcutaneous sponge wound model was used. Murine wound neutrophils were harvested at 24 and 120 h after injury and treated with physiological (10−9 M) and pharmacologic (10−6 M) doses of NE. Phagocytosis of green fluorescent protein-labeled Escherichia coli was assayed by flow cytometry. The signaling pathways mediating NE modulation of phagocytosis by wound neutrophils were defined by pharmacologic manipulation of α- and β-adrenoreceptors and protein kinase A.ResultsPharmacologic-dose NE, but not-physiological-dose NE, suppressed the phagocytic efficiency of 120-h wound neutrophils. This alteration in phagocytic efficiency appears to be mediated through alpha- and beta- adrenorecptors and downstream protein kinase A. Phagocytosis by 24-h wound neutrophils was not impacted by NE treatment.ConclusionsThe present study is the first to demonstrate NE-mediated alterations in the process of phagocytosis by wound neutrophils. We conclude that NE plays a temporally and dose-defined immunomodulatory role in cutaneous wound healing through alterations in phagocytosis by wound neutrophils and may represent a target for therapeutic manipulation of the innate immune response.