Reperfusion-Induced Low-Density Neutrophils Mediate Early Vascular Inflammation and Innate Reprogramming in Cardiac Grafts 2265648

Introduction The vascular endothelium acts as a mucosal-like barrier that regulates immune tolerance. During heart transplantation, ischemia—reperfusion injury (IRI) disrupts this barrier, exposing subendothelial antigens and activating innate responses. While neutrophils dominate early IRI, the significance of circulating low-density neutrophils (LDNs) remains unclear. We hypothesized that graft reperfusion induces a transient LDN surge that coordinates monocyte remodeling and defines a mucosal-vascular interface response similar to epithelial immune activation. Methods Eleven orthotopic heart-transplant recipients (mean 59.7 ± 6.3 y; BMI 27.0 ± 4.9; mixed gender; all DBD donors) were prospectively enrolled. Pulmonary-artery blood was collected pre-cross-clamp (Pre-Cx), post-reperfusion (Post-Cx), postoperative day 1, and 2 (POD-1 & 2), PBMC fractions were analyzed by flow cytometry to quantify LDNs (CD45+CD15+CD16+CD14⁻) and monocyte subsets–CM (CD14++CD16⁻), INT-M (CD14++CD16+), NCM (CD14+CD16++). Temporal shifts were assessed by repeated-measures ANOVA. Results LDNs were scarce Pre-Cx (5.4 ± 2.1%) but rose Post-Cx (25.3 ± 8.2%, p < 0.0001), peaked POD-1 (70.4 ± 9.8%, p < 0.0001), and declined POD-2 (34.9 ± 11.2%, p < 0.001). INT-M expanded (p < 0.001) while NCM fell >70% (p < 0.01). LDNs correlated with INT-M (r = 0.72, p = 0.004) and inversely with NCM (r = —0.65, p = 0.009). These kinetics parallel mucosal inflammation where activated neutrophils release IFN-β, CXCL9/10, and IL-10 to drive monocyte reprogramming and barrier repair Conclusion Reperfusion triggers a sterile mucosal-type cascade at the vascular interface, marked by an acute LDN surge and monocyte transition toward intermediate, reparative phenotypes. This neutrophil—monocyte axis links endothelial injury with early graft inflammation, defining an innate checkpoint that bridges vascular barrier immunity and transplant tolerance. LDNs represent a transient mucosal signature and potential biomarker of reperfusion-driven immune activation Funding Source n/a Topic Categories Mucosal and Regional Immunology (MUC)