Monophosphoryl lipid A boosts macrophage antimicrobial immunity by metabolically regulating source-specific ROS...

Area of Science:

• Immunology
• Metabolic pathways
• Host-directed therapy

Background:

• Monophosphoryl lipid A (MPLA) is a toll-like receptor (TLR) 4 agonist and vaccine adjuvant.
• MPLA activates innate immune cells for pathogen protection.
• Metabolic and molecular adaptations underlying MPLA's immune response are not well understood.

Purpose of the Study:

• To investigate the sources of reactive oxygen species (ROS) contributing to MPLA-induced macrophage antimicrobial activity.
• To identify metabolic and redox adaptations supporting MPLA's immune effects.
• To explore MPLA's potential beyond vaccine adjuvancy.

Main Methods:

• Used genetic deletion and pharmacologic inhibition to assess ROS sources (NADPH oxidase 2 (NOX2), xanthine oxidase (XO), mitochondria, inducible nitric oxide synthase (iNOS)).
• Analyzed oxidative pentose phosphate pathway (oxPPP) activity, glutathione systems, and mitochondrial oxidative phosphorylation.
• Assessed macrophage clearance of *Pseudomonas aeruginosa*.

Main Results:

• MPLA enhanced bacterial clearance by coordinating ROS generation, with NOX2 being essential.
• XO provided auxiliary ROS, acting additively with NOX2.
• MPLA activated oxPPP for NADPH production, supporting phagocytosis and redox homeostasis.
• Mitochondrial ROS were constrained by antioxidant systems and dispensable for protection.
• iNOS-derived nitric oxide did not contribute to the antimicrobial phenotype.

Conclusions:

• MPLA reprograms innate immunity by coordinating specific ROS sources and metabolic adaptations.
• MPLA's mechanisms involve NOX2-dependent ROS generation and oxPPP activation.
• Findings support MPLA's potential as a host-directed antimicrobial therapy.