Docosahexaenoic acid supplementation inhibits monocyte exhaustion memory formation during sepsis

Docosahexaenoic acid (DHA) is an omega-3 fatty acid with important roles in inflammation resolution. We tested the impact of DHA supplementation on monocyte exhaustion, an immune memory state contributing to chronic inflammation and immunosuppression following sepsis. Ex vivo sepsis modeling was performed with C57BL/6 mouse bone marrow monocytes (BMMCs) and peripheral blood mononuclear cells (PBMCs) from septic patients. BMMCs stimulated with lipopolysaccharide (100 ng/mL) for 5 days were supplemented with 60 µM DHA. Septic patient PBMCs were treated for 24 h with 0, 15, 30, 45, or 60 µM DHA. Monocyte exhaustion was assayed by flow cytometry, qRT-PCR, and cytometric arrays. DNA methylation changes linked to exhaustion memory were measured by bisulfite pyrosequencing. Western blots were performed to link DHA treatment to altered cell signaling pathways in septic monocytes. DHA supplementation suppresses the expression major exhaustion regulators CD38 and PD-L1 and dampens inflammatory cytokine transcription. These effects were mechanistically linked to STAT1/3 inhibition and accompanied by altered DNA methylation at immune regulators. DHA treatment also reduced CD157 cell surface levels and CCL2 secretion, both contributors to tissue invasion and injury during sepsis. Our results support the therapeutic application of DHA for the prevention of chronic immune dysfunction in sepsis survivors.