Neutrophilia and neutrophil-derived extracellular traps as innate immune markers of SARS-CoV-2 infection in a feline animal model

Excessive neutrophil recruitment and dysregulation contribute to worsened clinical outcomes in hospitalized COVID-19 patients. Targeting this dysregulated response offers therapeutic potential in the treatment of SARS-CoV-2 infections which can be enhanced by the availability of reliable, translational animal models for disease. Domestic cats are naturally infected and exhibit clinical disease similar to that seen in COVID-19. Utilizing our previously developed feline model for COVID-19, we hypothesize that neutrophil dysregulation and the release of neutrophil extracellular traps (NETs) significantly worsen pulmonary damage in domestic cats. Specific-pathogen-free cats (n=12) were inoculated with SARS CoV-2 (B.1.617.2) or vehicle (n=6). Plasma, bronchoalveolar lavage, and tissues were collected over 12 days. Detection of NETs using MPO-DNA ELISA and Quant-iT PicoGreen® dsDNA assay indicate significant elevations at 4dpi and 8dpi in the plasma as compared to vehicle, with the peak NETs detection at 4dpi(p<0.05). These findings were similarly evident in the BAL fluid of infected versus vehicle-inoculated cats(p<0.05). Immunohistochemistry of respiratory tissues utilizing three major markers of activated neutrophils and NETS; citrullinated histone 3, MPO, and neutrophil elastase, show marked amplifications compared to vehicle. These findings co-localize to areas of significant pulmonary damage. Elucidating these innate markers and their functional changes provides insight into understanding the immunopathogenesis and potential therapeutic interventions in SARS-CoV-2 infection. These data enforce the role of domestic cats as a flexible translational model to develop these interventions. NIH-NIGMS (P20GM103648)