ABSTRACT
Emerging data indicate that complement and neutrophils contribute to the maladaptive immune response that fuels hyperinflammation and thrombotic microangiopathy, thereby increasing coronavirus 2019 (COVID-19) mortality. Here, we investigated how complement interacts with the platelet/neutrophil extracellular traps (NETs)/thrombin axis, using COVID-19 specimens, cell-based inhibition studies, and NET/human aortic endothelial cell (HAEC) cocultures. Increased plasma levels of NETs, tissue factor (TF) activity, and sC5b-9 were detected in patients. Neutrophils of patients yielded high TF expression and released NETs carrying active TF. Treatment of control neutrophils with COVID-19 platelet-rich plasma generated TF-bearing NETs that induced thrombotic activity of HAECs. Thrombin or NETosis inhibition or C5aR1 blockade attenuated platelet-mediated NET-driven thrombogenicity. COVID-19 serum induced complement activation in vitro, consistent with high complement activity in clinical samples. Complement C3 inhibition with compstatin Cp40 disrupted TF expression in neutrophils. In conclusion, we provide a mechanistic basis for a pivotal role of complement and NETs in COVID-19 immunothrombosis. This study supports strategies against severe acute respiratory syndrome coronavirus 2 that exploit complement or NETosis inhibition.
Subject(s)
Betacoronavirus , Complement Membrane Attack Complex , Coronavirus Infections , Extracellular Traps , Neutrophils , Pandemics , Pneumonia, Viral , Thromboplastin , Thrombosis , Aged , Betacoronavirus/immunology , Betacoronavirus/metabolism , COVID-19 , Complement Activation/drug effects , Complement Membrane Attack Complex/immunology , Complement Membrane Attack Complex/metabolism , Coronavirus Infections/blood , Coronavirus Infections/immunology , Extracellular Traps/immunology , Extracellular Traps/metabolism , Female , Humans , Male , Middle Aged , Neutrophils/immunology , Neutrophils/metabolism , Peptides, Cyclic/pharmacology , Pneumonia, Viral/blood , Pneumonia, Viral/immunology , Receptor, Anaphylatoxin C5a/antagonists & inhibitors , Receptor, Anaphylatoxin C5a/blood , Receptor, Anaphylatoxin C5a/immunology , Respiratory Distress Syndrome/blood , Respiratory Distress Syndrome/immunology , Respiratory Distress Syndrome/virology , SARS-CoV-2 , Thrombin/immunology , Thrombin/metabolism , Thromboplastin/immunology , Thromboplastin/metabolism , Thrombosis/blood , Thrombosis/immunology , Thrombosis/virologyABSTRACT
BACKGROUND: Prognostic markers for disease severity and identification of therapeutic targets in COVID-19 are urgently needed. We have studied innate and adaptive immunity on protein and transcriptomic level in COVID-19 patients with different disease severity at admission and longitudinally during hospitalization. METHODS: Peripheral blood mononuclear cells (PBMCs) were collected at three time points from 31 patients included in the Norwegian SARS-CoV-2 cohort study and analysed by flow cytometry and RNA sequencing. Patients were grouped as either mild/moderate (n = 14), severe (n = 11) or critical (n = 6) disease in accordance with WHO guidelines and compared with patients with SARS-CoV-2-negative bacterial sepsis (n = 5) and healthy controls (n = 10). RESULTS: COVID-19 severity was characterized by decreased interleukin 7 receptor alpha chain (CD127) expression in naïve CD4 and CD8 T cells. Activation (CD25 and HLA-DR) and exhaustion (PD-1) markers on T cells were increased compared with controls, but comparable between COVID-19 severity groups. Non-classical monocytes and monocytic HLA-DR expression decreased whereas monocytic PD-L1 and CD142 expression increased with COVID-19 severity. RNA sequencing exhibited increased plasma B-cell activity in critical COVID-19 and yet predominantly reduced transcripts related to immune response pathways compared with milder disease. CONCLUSION: Critical COVID-19 seems to be characterized by an immune profile of activated and exhausted T cells and monocytes. This immune phenotype may influence the capacity to mount an efficient T-cell immune response. Plasma B-cell activity and calprotectin were higher in critical COVID-19 while most transcripts related to immune functions were reduced, in particular affecting B cells. The potential of these cells as therapeutic targets in COVID-19 should be further explored.