Monocyte Oxidative Stress Underlies Persistent Immune Activation in Long COVID Postural Orthostatic Tachycardia Syndrome.

Long COVID Postural Orthostatic Tachycardia Syndrome (LCPOTS) is characterized by persistent orthostatic tachycardia and systemic symptoms following SARS-CoV-2 infection. Many features of LCPOTS suggest ongoing immune activation, but the mechanisms driving this response remain unclear. In this study, we show that patients with LCPOTS, compared with individuals who recovered from SARS-CoV-2 without POTS, exhibit increased monocyte mitochondrial content and superoxide production, along with downregulation of NRF2-dependent antioxidant enzymes. This is accompanied by a marked increase in the formation of isolevuglandins (IsoLGs) in monocytes, which modify self-proteins and act as neoantigens capable of activating T cells. Consistent with this, LCPOTS patients exhibit a 3-fold increase in circulating T cell-monocyte doublets with immunological synapse formation. T cells in these complexes display a proinflammatory effector-memory and TEMRA phenotype, producing IFN-γ and IL-17A, which correlated with symptom severity. Circulating cytokines, including IL-17A, IFN-γ, and TNF-α, are elevated in patients with LCPOTS. In a subset of patients, transcutaneous vagal nerve stimulation (t-VNS) reduced circulating CD3 + CD14 + doublets, IsoLG accumulation, and IL-6 expression in CD14 + monocytes. Our findings suggest that reduced vagal tone in LCPOTS leads to monocyte oxidative stress, IsoLG neoantigen formation, and T cell activation, linking immune dysregulation to cardiovagal dysfunction. Targeting these pathways may offer novel therapeutic opportunities.