Severe COVID-19 patients develop acute respiratory distress syndrome that may progress to cytokine storm syndrome, organ dysfunction, and death. Considering that neutrophil extracellular traps (NETs) have been described as important mediators of tissue damage in inflammatory diseases, we investigated whether NETs would be involved in COVID-19 pathophysiology. A cohort of 32 hospitalized patients with a confirmed diagnosis of COVID-19 and healthy controls were enrolled. The concentration of NETs was augmented in plasma, tracheal aspirate, and lung autopsies tissues from COVID-19 patients, and their neutrophils released higher levels of NETs. Notably, we found that viable SARS-CoV-2 can directly induce the release of NETs by healthy neutrophils. Mechanistically, NETs triggered by SARS-CoV-2 depend on angiotensin-converting enzyme 2, serine protease, virus replication, and PAD-4. Finally, NETs released by SARS-CoV-2–activated neutrophils promote lung epithelial cell death in vitro. These results unravel a possible detrimental role of NETs in the pathophysiology of COVID-19. Therefore, the inhibition of NETs represents a potential therapeutic target for COVID-19.

Severe cases of COVID-19 are characterized by a strong inflammatory process that may ultimately lead to organ failure and patient death. The NLRP3 inflammasome is a molecular platform that promotes inflammation via cleavage and activation of key inflammatory molecules including active caspase-1 (Casp1p20), IL-1β, and IL-18. Although participation of the inflammasome in COVID-19 has been highly speculated, the inflammasome activation and participation in the outcome of the disease are unknown. Here we demonstrate that the NLRP3 inflammasome is activated in response to SARS-CoV-2 infection and is active in COVID-19 patients. Studying moderate and severe COVID-19 patients, we found active NLRP3 inflammasome in PBMCs and tissues of postmortem patients upon autopsy. Inflammasome-derived products such as Casp1p20 and IL-18 in the sera correlated with the markers of COVID-19 severity, including IL-6 and LDH. Moreover, higher levels of IL-18 and Casp1p20 are associated with disease severity and poor clinical outcome. Our results suggest that inflammasomes participate in the pathophysiology of the disease, indicating that these platforms might be a marker of disease severity and a potential therapeutic target for COVID-19.

Rationale: Sepsis is defined as a systemic inflammatory response to infection, which in its severe form is associated with multiple organ dysfunction syndrome (MODS). The precise mechanisms by which MODS develops remain unclear. Neutrophils have a pivotal role in the defense against infections; however, overwhelming activation of neutrophils is known to elicit tissue damage. Objectives: We investigated the role of the chemokine receptor CCR2 in driving neutrophil infiltration and eliciting tissue damage in remote organs during sepsis. Methods: Sepsis was induced in wild-type mice treated with CCR2 antagonist (RS504393) or CCR2^−/− mice by cecal ligation and puncture (CLP) model. Neutrophil infiltration into the organs was measured by myeloperoxidase activity and fluorescence-activated cell sorter. CCR2 expression and chemotaxis were determined in neutrophils stimulated with Toll-like receptor agonists or isolated from septic mice and patients. Measurements and Main Results: CCR2 expression and responsiveness to its ligands was induced in circulating neutrophils during CLP-induced sepsis by a mechanism dependent on Toll-like receptor/nuclear factor-κB pathway. Genetic or pharmacologic inhibition of CCR2 protected mice from CLP-induced mortality. This protection was associated with lower infiltration of neutrophils into the lungs, heart, and kidneys and reduced serum biochemical indicators of organ injury and dysfunction. Importantly, neutrophils from septic patients express high levels of CCR2, and the severity of patient illness correlated positively with increasing neutrophil chemotaxis to CCR2 ligands. Conclusions: Collectively, these data identify CCR2 as a key receptor that drives the inappropriate infiltration of neutrophils into remote organs during sepsis. Therefore, CCR2 blockade is a novel potential therapeutic target for treatment of sepsis-induced MODS.

The deregulation of inflammatory response during sepsis seems to reflect the overproduction of mediators, which suppress leukocyte functions. We investigated the intracellular mechanisms underlying the inability of neutrophils from severe septic patients to migrate toward chemoattractants. Patients with sepsis (52) and 15 volunteers were prospectively enrolled. Patients presented increased circulating levels of tumor necrosis factor-α, interferon-γ, interleukin (IL)–8, and IL-10. Patients showed reduced neutrophil chemotaxis to formyl-methionyl-leucyl-phenylalanine (FMLP), leukotriene B₄ (LTB₄) or IL-8. No difference in the transcription or expression of the IL-8 receptor, CXCR1, was detected in neutrophils from controls and patients. However, septic neutrophils failed to increase tyrosine phosphorylation and actin polymerization in response to IL-8 or LTB₄. In contrast, septic neutrophils, similar to controls, showed phagocytic activity that induced actin polymerization and augmented phosphotyrosine content. Treatment of control neutrophils with cytokines and lipopolysaccharide (LPS) to mimic endogenous septic environment inhibited actin polymerization and tyrosine phosphorylation in response to IL-8 or LTB₄. High expression of G protein–coupled receptor kinase 2 (GRK2) and GRK5 was detected in septic neutrophils and control cells treated with cytokines plus LPS. Data suggest that endogenous mediators produced during sepsis might continually activate circulating neutrophils, leading to GRK activation, which may induce neutrophil desensitization to chemoattractants.

Several prognostic indices have been employed to predict the outcome of surgical critically ill patients. Among them, acute physiology and chronic health evaluation (APACHE) II, sequential organ failure assessment (SOFA) and simplified acute physiology score (SAPS 3) are widely used. It seems that biological markers such as C-reactive protein (CRP), albumin, and blood lactate levels correlate with the degree of inflammation during the immediate postoperative phase and could be used as independent predictors. The objective of this study is to compare the different predictive values of prognostic indices and biological markers in the outcome of 847 surgical patients admitted to the intensive care unit (ICU) in the postoperative phase. The patients were divided into survivors (n = 765, 57.4% males, age 61, interquartile range 51–71) and nonsurvivors (n = 82, 57.3% males, age 70, interquartile range 58–79). APACHE II, APACHE II death probability (DP), SOFA, SAPS 3, SAPS 3 DP, CRP, albumin, and lactate were recorded on ICU admission (first 24 hours). The area under the ROC curve (AUROC) and 95% confidence interval (95% CI) were used to measure the index accuracy to predict mortality. The AUROC and 95% CI for APACHE II, APACHE II DP, SOFA, SAPS 3, SAPS 3 DP, CRP/albumin ratio, CRP, albumin, and lactate were 0.850 (0.824–0.873), 0.855 (0.829–0.878), 0.791 (0.762–0.818), 0.840 (0.813–0.864), 0.840 (0.813–0.864), 0.731 (0.700–0.761), 0.708 (0.676–0.739), 0.697 (0.665–0.728), and 0.601 (0.567–0.634), respectively. The ICU and overall in-hospital mortality were 6.6 and 9.7%, respectively. The APACHE II, APACHE II DP, SAPS 3, SAPS 3 DP, and SOFA scores showed a better performance than CRP/albumin ratio, CRP, albumin, or lactate to predict in-hospital mortality of surgical critically ill patients. Even though all indices were able to discriminate septic from nonseptic patients, only APACHE II, APACHE II DP, SOFA and to a lesser extent SAPS 3, SAPS 3 DP, and blood lactate levels could predict in the first 24-hour ICU admission surgical patients who have survived sepsis.