Oxidant alterations in CD16 expression are cytoskeletal induced

Area of Science:

• Immunology
• Cell Biology
• Biochemistry

Background:

• Ischemia-reperfusion injury induces oxidative stress.
• Oxidative stress alters circulating monocyte phenotype from CD14++CD16- to CD14+CD16+.
• This phenotypic shift is linked to altered immunity and organ failure, but the mechanism is unclear.

Purpose of the Study:

• To investigate the mechanism of oxidative stress-induced monocyte phenotypic changes.
• To test the hypothesis that intracellular calcium flux, cytoskeletal changes, and lipid raft alterations mediate this transformation.
• To model these changes using hydrogen peroxide (H2O2) exposure in vitro.

Main Methods:

• Human peripheral blood monocytes were exposed to 100 mM H2O2 for up to 24 hours.
• Cells were pretreated with inhibitors of actin polymerization (cytochalasin D, lactrunculin A) or calcium flux (1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid).
• Fluorescence-activated cell sorting, immunoblotting, and confocal microscopy were used to analyze CD14, CD16, cytokine expression, and lipid raft localization.

Main Results:

• H2O2 exposure significantly increased surface CD16 expression on monocytes over time.
• Total cellular CD16 remained unchanged, but its localization shifted to lipid rafts, with decreased intracellular levels.
• Increased CD16 expression correlated with elevated TNF-alpha, altered actin polymerization, and raft macrodomain formation, all inhibited by actin and calcium blockers.

Conclusions:

• Oxidative stress induces monocyte phenotypic changes via calcium flux-mediated cytoskeletal and lipid raft alterations.
• This mechanism explains the shift to CD14+CD16+ proinflammatory monocytes during reperfusion.
• Findings suggest a novel pathway distinct from simple demargination or bone marrow-derived monocyte production.