The SARS-CoV-2 virus caused a worldwide epidemic of respiratory disease (COVID-19). Acute respiratory distress syndrome (ARDS) has been associated with severe COVID-19. Activation of neutrophils have been linked to ARDS in COVID-19. While emerging results indicate that SARS-CoV-2 leads to neutrophil activation, it remains unknown which components of the virus are responsible for this. We assessed in vitro how the spike (S) protein and anti-spike antibodies affect neutrophils. Human neutrophils were isolated from healthy donors. Different concentrations of recombinant S protein, a monoclonal antibody (mAb) produced against the S protein and their immunocomplex were used to stimulate neutrophils. Unstimulated and PMA-treated neutrophils were used as negative and positive controls. Reactive oxygen species (ROS) production was measured by Diogenes chemiluminescence, and cell death was measured by fluorescence. While no significant increase of cell death was observed, neutrophils responded with a dose-dependent increase in the production of ROS when stimulated with either the S protein or the mAb. Neutrophils produced significantly (p<0.05) more ROS when activated by 1,000 ng of the mAb. Immune complex stimulation (1,000 ng each component) of human neutrophils also lead to significantly (p<0.005) enhanced ROS production compared to stimulations by the protein or the mAb alone. Neutrophil cell death was also significantly enhanced when stimulated by the immune complex (500 ng and 1,000 ng each component) (p<0.05, p<0.005, respectively). Our work indicates that the S protein and its immune complex formed with mAb could stimulate neutrophils in vitro and contribute to neutrophil-mediated tissue damage in COVID-19 patients.

Supported by grants from: Oswaldo Cruz Foundation, International Graduate Programme (PrInt FIOCRUZ-CAPES), University of Georgia and NIH.