Human microparticles generated during sepsis in patients with critical illness are neutrophil-derived and modulate the immune response

BACKGROUND: Microparticles (MPs) are 0.3 Km to 1.0 Km vesicles generated after cell activation or apoptosis that may play a role in the pathophysiology of sepsis. We sought to elucidate the role of MPs in patients with critical illness and hypothesized that MPs are generated at the site of inflammation and can modulate the immune response. METHODS: Surgical patients with critical illness with ongoing sepsis were enrolled from the intensive care unit of an urban, Level I trauma center from March to June 2011. Abdominal washings and bronchoalveolar lavage fluid were collected from sites of inflammation. MPs were isolated using differential centrifugation, then characterized by flow cytometry. Immunologic assays were conducted by incubating neutrophil-derived MPs (NDMPs) with a human monocytic cell line (THP-1). A p value <= 0.05 was considered significant. RESULTS: MPs were absent in noninflamed foci in patients, whereas NDMPs were present in locations of inflammation. NDMPs were added to cultured THP-1 cells to quantify immunomodulatory effects. THP-1 cells were able to phagocytose NDMPs. Cells that ingested NDMPs demonstrated increased activation. In contrast, bystander THP-1 cells without ingested NDMPs demonstrated decreased activation. CONCLUSION: NDMPs are generated at the site of inflammation in patients with critical illness during sepsis. They have a divergent effect on the immune response by activating phagocytic cells and deactivating bystander cells. NDMPs may play an important role in regulating the inflammatory response to sepsis in patients with critical illness. (J Trauma Acute Care Surg. 2012; 73: 401-407. Copyright (C) 2012 by Lippincott Williams & Wilkins) LEVEL OF EVIDENCE: Prognostic/epidemiologic study, level III.