Self-sustaining IL-8 loops drive a prothrombotic neutrophil phenotype in severe COVID-19

Kaiser, Rainer; Leunig, Alexander; Pekayvaz, Kami; Popp, Oliver; Joppich, Markus; Polewka, Vivien; Escaig, Raphael; Anjum, Afra; Hoffknecht, Marie-Louise; Gold, Christoph; Brambs, Sophia; Engel, Anouk; Stockhausen, Sven; Knottenberg, Viktoria; Titova, Anna; Haji, Mohamed; Scherer, Clemens; Muenchhoff, Maximilian; Hellmuth, Johannes C.; Saar, Kathrin; Schubert, Benjamin; Hilgendorff, Anne; Schulz, Christian; Kääb, Stefan; Zimmer, Ralf; Hübner, Norbert; Massberg, Steffen; Mertins, Philipp; Nicolai, Leo; Stark, Konstantin

Neutrophils provide a critical line of defense in immune responses to various pathogens, inflicting self-damage upon transition to a hyperactivated, procoagulant state. Recent work has highlighted proinflammatory neutrophil phenotypes contributing to lung injury and acute respiratory distress syndrome (ARDS) in patients with coronavirus disease 2019 (COVID-19). Here, we use state-of-the art mass spectrometry–based proteomics and transcriptomic and correlative analyses as well as functional in vitro and in vivo studies to dissect how neutrophils contribute to the progression to severe COVID-19. We identify a reinforcing loop of both systemic and neutrophil intrinsic IL-8 (CXCL8/IL-8) dysregulation, which initiates and perpetuates neutrophil-driven immunopathology. This positive feedback loop of systemic and neutrophil autocrine IL-8 production leads to an activated, prothrombotic neutrophil phenotype characterized by degranulation and neutrophil extracellular trap (NET) formation. In severe COVID-19, neutrophils directly initiate the coagulation and complement cascade, highlighting a link to the immunothrombotic state observed in these patients. Targeting the IL-8–CXCR-1/-2 axis interferes with this vicious cycle and attenuates neutrophil activation, degranulation, NETosis, and IL-8 release. Finally, we show that blocking IL-8–like signaling reduces severe acute respiratory distress syndrome of coronavirus 2 (SARS-CoV-2) spike protein–induced, human ACE2–dependent pulmonary microthrombosis in mice. In summary, our data provide comprehensive insights into the activation mechanisms of neutrophils in COVID-19 and uncover a self-sustaining neutrophil–IL-8 axis as a promising therapeutic target in severe SARS-CoV-2 infection.