Hiroshi Ueki, DVM, PhD: No financial relationships to disclose
Introduction/Rationale: Microthrombus formation is a determinant of COVID-19 severity; however, the in vivo spatiotemporal mechanisms of thrombogenesis remain unclear. Here, we used an in vivo imaging system to elucidate the dynamics of neutrophils and platelets in the pulmonary microcirculation and to understand how SARS-CoV-2 infection compromises lung perfusion. Methods
Methods: We used in vivo two-photon excitation microscopy in a Biosafety Level 3 facility to visualize cellular pathophysiology in Ob/Ob (obesity model) mice infected with a fluorescent-reporter SARS-CoV-2 virus. We quantified intravascular neutrophil motility, platelet aggregate size, and pulmonary capillary perfusion. Adhesion molecule expression on lung neutrophils was assessed with flow cytometry. Clinical relevance was validated by re-analyzing scRNA-seq datasets of peripheral neutrophils from COVID-19 patients.
Results: In vivo imaging revealed that SARS-CoV-2 infection significantly prolonged neutrophil adhesion to pulmonary vessel walls in Ob/Ob mice. This stagnation was driven by upregulated CD44, CD62L, and E-selectin on neutrophils. Adherent neutrophils frequently captured platelets, forming complexes that evolved into microthrombi and impaired pulmonary perfusion. Neutrophil depletion reduced thrombus formation and extended survival. Human scRNA-seq data analysis confirmed elevated CD44 and SELL (CD62L) expression in neutrophils from severe COVID-19 cases.
Conclusion: We found that upregulated adhesion molecules on intravascular neutrophils trigger vessel wall adhesion, acting as scaffolds for platelet aggregation. This cascade drives microthrombus formation and pulmonary perfusion defects, highlighting neutrophil adhesion as a therapeutic target for severe COVID-19.
