Ferric Ammonium Citrate Upregulates PD-L1 Expression through Generation of Reactive Oxygen Species

Area of Science:

• Immunology
• Cell Biology
• Metabolism

Background:

• Iron is crucial for macrophage polarization, affecting metabolic and redox states.
• The precise impact of iron on macrophage immune status remains debated.
• Ferric ammonium citrate (FAC) is a common iron supplement with potential immunomodulatory effects.

Purpose of the Study:

• To investigate the effect of ferric ammonium citrate (FAC) on macrophage phenotype and immune status.
• To elucidate the mechanisms underlying FAC-induced changes in macrophages, focusing on metabolism and redox balance.
• To explore the link between iron overload, reactive oxygen species (ROS), and PD-L1 expression in macrophages.

Main Methods:

• Macrophage culture and treatment with FAC.
• Analysis of macrophage phenotype and T cell subset enrichment.
• Measurement of oxygen consumption rate (OCR) and aconitase activity.
• Assessment of Fenton reaction and ROS production.
• Inhibition of ROS production using ferrostatin, rotenone, and N-acetyl-L-cysteine.

Main Results:

• FAC upregulated programmed death-ligand 1 (PD-L1) expression in macrophages.
• FAC treatment altered macrophage phenotype and enriched immune-modulatory T cell subsets.
• FAC enhanced mitochondrial metabolic processes, including oxygen consumption rate (OCR).
• FAC accelerated the Fenton reaction, increasing ROS production.
• ROS production was confirmed as the key mediator of FAC-induced PD-L1 expression.

Conclusions:

• Iron overload via FAC upregulates PD-L1 in macrophages through enhanced metabolism and ROS generation.
• Metabolic and redox regulation are critical for FAC-mediated PD-L1 expression.
• Understanding iron's role in ROS production offers potential strategies for cancer immunotherapy.