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Neutrophil activation in sepsis. The relationship between fmet-leu-phe receptor mobilization and oxidative activity
1Department of Surgery, University of Cincinnati College of Medicine, OH 45267-0558.
Abstract:
To elucidate further the manifestations and mechanisms of neutrophil (PMN) activation, PMNs from control and septic subjects were studied at baseline and under conditions of graded, in vitro activation. At baseline (4 degrees C PMN isolation), septic-derived PMNs were activated, as manifested by twofold increases in fmet-leu-phe (FMLP)-induced oxidative activity and concomitant FMLP surface receptor expression, compared with controls. Following degranulationlike maximal activation (phorbol myristate acetate pretreatment), both PMN populations exhibited maximal FMLP-induced oxidative priming and receptor up-regulation. However, following exudation-like moderate activation (37 degrees C pretreatment), control PMNs underwent significant receptor mobilization and oxidative priming but septic-derived PMNs exhibited oxidative deactivation (decreased FMLP-induced oxidative activity) without changes in FMLP receptor expression. Our data support the theory that while circulating PMNs in sepsis may promote oxidant-related microvascular lung injury, their oxidative deactivation following transpulmonary exudation (simulated by 37 degrees C pretreatment) may underlie the increased incidence of pulmonary infections seen in sepsis-induced adult respiratory distress syndrome.
Insights
Neutrophils (PMNs) from septic patients show heightened activation at baseline but paradoxical oxidative deactivation after simulated exudation. This altered response in sepsis may increase susceptibility to lung infections in acute respiratory distress syndrome.
Area of Science:
- Immunology
- Cell Biology
- Critical Care Medicine
Background:
- Neutrophil (PMN) activation is crucial in host defense but dysregulated in sepsis.
- Sepsis-associated acute respiratory distress syndrome (ARDS) involves complex inflammatory processes and increased infection risk.
Purpose of the Study:
- To investigate neutrophil activation patterns in sepsis under varying in vitro conditions.
- To elucidate the mechanisms behind altered neutrophil function in septic patients.
Main Methods:
- Neutrophils were isolated from control and septic subjects.
- Cells were studied at baseline (4°C) and after graded in vitro activation simulating degranulation (maximal) and exudation (moderate, 37°C).
- FMLP-induced oxidative activity and FMLP surface receptor expression were measured.
Main Results:
- Septic neutrophils exhibited higher baseline FMLP-induced oxidative activity and receptor expression compared to controls.
- Both groups showed maximal activation after phorbol myristate acetate pretreatment.
- Moderate activation at 37°C led to oxidative deactivation in septic neutrophils, unlike controls, with no change in FMLP receptor expression.
Conclusions:
- Circulating neutrophils in sepsis may contribute to oxidant-related lung injury.
- Oxidative deactivation of neutrophils following exudation in sepsis could explain the increased incidence of pulmonary infections in ARDS.
- Understanding these neutrophil dysfunctions is key to managing sepsis-induced lung complications.