Administration of a CXCR2 antagonist, SCH527123, together with oseltamivir suppresses NETosis and protects mice from lethal influenza and piglets from swine-influenza infection.

Excessive neutrophil influx, their released neutrophil extracellular traps (NETs) and extracellular histones are associated with disease severity in influenza-infected patients. Neutrophil chemokine receptor CXCR2 is a critical target for suppressing neutrophilic inflammation. Here, we investigated temporal dynamics of neutrophil activity and NETosis to determine the optimal timing of treatment with the CXCR2 antagonist, SCH527123 and we tested its efficacy together with antiviral agent, oseltamivir in murine and piglet influenza-pneumonia models. Our studies revealed that SCH527123 plus oseltamivir markedly improved survival of mice infected with lethal-influenza, and diminished lung pathology in swine-influenza-infected piglets. Mechanistically, addition of SCH527123 in the combination treatment attenuated neutrophil influx, NETosis in both mice and piglets. Further, neutrophils isolated from influenza-infected mice showed greater susceptibility to NETotic death when stimulated with a CXCR2 ligand, IL-8. In addition, CXCR2-stimulation induced nuclear translocation of neutrophil elastase, and enhanced citrullination of histones that triggers chromatin decondensation during NETs formation. Studies on temporal dynamics of neutrophils and NETs during influenza thus provide important insights into the optimal timing of CXCR2 antagonist treatment for attenuating neutrophil-mediated lung pathology. These findings reveal that pharmacological treatment with CXCR2 antagonist plus antiviral agent could significantly ameliorate morbidity and mortality in virulent and sub-lethal influenza infections.