Cytokine release syndrome (CRS) is a life-threatening complication induced by systemic inflammatory responses to infections, including bacteria and chimeric antigen receptor T cell therapy. There are currently no immunotherapies with proven clinical efficacy and understanding of the molecular mechanisms of CRS pathogenesis is limited. Here, we found that patients diagnosed with CRS from sepsis, acute respiratory distress syndrome (ARDS), or burns showed common manifestations: strikingly elevated levels of the four proinflammatory cytokines interleukin (IL)-6, IL-8, monocyte chemotactic protein-1 (MCP-1), and IL-10 and the coagulation cascade activator plasminogen activator inhibitor-1 (PAI-1). Our in vitro data indicate that endothelial IL-6 trans-signaling formed an inflammation circuit for robust IL-6, IL-8, and MCP-1 production and promoted PAI-1 production; additionally, an IL-6 signaling blockade by the human monoclonal antibody tocilizumab blunted endothelial cell activation. Plasma from severe COVID-19 patients similarly exhibited increased IL-6, IL-10, and MCP-1 levels, but these levels were not as high as those in patients with CRS from other causes. In contrast, the PAI-1 levels in COVID-19 patients were as highly elevated as those in patients with bacterial sepsis or ARDS. Tocilizumab treatment decreased the PAI-1 levels and alleviated critical illness in severe COVID-19 patients. Our findings suggest that distinct levels of cytokine production are associated with CRS induced by bacterial infection and COVID-19, but both CRS types are accompanied by endotheliopathy through IL-6 trans-signaling. Thus, the present study highlights the crucial role of IL-6 signaling in endothelial dysfunction during bacterial infection and COVID-19.

Sepsis remains a major cause of death. Cytokines interact closely with each other and play a crucial role in the progression of sepsis. We focussed on the associations of a cytokine network with prognosis and disease severities in sepsis. This retrospective study included 31 patients with sepsis and 13 healthy controls. Blood samples were collected from patients on days 1, 2, 4, 6, 8, 11 and 15 and from healthy controls. Levels of PAI-1, IFN-α, IFN-γ, IL-1β, IL-6, IL-8, IL-12/IL-23p40, IL-17A, TNF-α, MCP-1, IL-4 and IL-10 were measured. SOFA, JAAM DIC and ISTH DIC scores were evaluated at the same times blood samples were taken. Network analysis revealed a network formed by PAI-1, IL-6, IL-8, MCP-1 and IL-10 on days 1, 2 and 4 throughout the acute phase of sepsis. There were positive correlations of each cytokine and the combined score (IL-6 + IL-8 + IL-10 + MCP-1) with the SOFA, JAAM DIC and ISTH DIC scores throughout the acute phase. A Cox proportional hazards model focussed on the acute phase showed that the above combined score was significantly related with patient prognosis, suggesting that the cytokine network of IL-6, IL-8, MCP-1 and IL-10 could play a pivotal role in the acute phase of sepsis.

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Sepsis-induced disseminated intravascular coagulation (DIC) is a major cause of death in patients admitted to intensive care units. Endothelial injury with microparticle production is reported in the pathogenesis of sepsis. Endothelial microparticles (EMPs) present several cell-specific surface antigens with different bioactivities, for example, tissue factor (TF), thrombomodulin (TM), and endothelial protein C receptor (EPCR). We investigated associations between these three different surface antigen–positive EMPs and sepsis-induced DIC. This cross-sectional study composed of 24 patients with sepsis and 23 healthy controls was conducted from November 2012 to September 2013. Blood samples were collected from patients within 24 h of diagnosis of severe sepsis and from healthy controls. Numbers of TF-positive EMPs (TF+ EMPs), TM-positive EMPs (TM+ EMPs), and EPCR-positive EMPs (EPCR+ EMPs) were measured by flow cytometry immediately thereafter. Acute Physiology and Chronic Health Evaluation II and Sequential Organ Failure Assessment scores were assessed in the severe sepsis patients at enrollment. We assessed DIC with the International Society of Thrombosis and Haemostasis (ISTH) overt DIC diagnostic criteria algorithm. Numbers of antigen-positive EMPs were increased significantly in both severe sepsis patients and controls and with the increase in ISTH DIC score. Numbers of TF+ EMPs and EPCR+ EMPs correlated significantly with Sequential Organ Failure Assessment score, and numbers of EPCR+ EMPs correlated significantly with Acute Physiology and Chronic Health Evaluation II score. Numbers of the three antigen-positive EMPs were increased significantly in severe sepsis patients versus those in healthy controls and with the increase of ISTH DIC score, suggesting that the specific bioactivity of each antigen-positive EMP may play a role in the progression of sepsis-induced DIC.

Major burns elicit an acute inflammatory response including various inflammatory cytokines. Cytokines play mutual interacting roles in inflammatory diseases. There is little evidence of the clinical significance of the cytokine network in patients with major burns. This study aimed to investigate the clinical significance of the cytokine network in patients with major burn. This prospective observational study comprising 38 patients with major burns (total body surface area (%TBSA) ≥ 20%) and 12 healthy controls was conducted from April 2014 to December 2016. Blood samples were collected from patients at six points: day 1, day 2, days 3-5, 1 week, 2 weeks and 1 month after the burn injury. Inflammatory cytokines (IFN-α, IFN-γ, IL-1β, IL-6, IL-8, IL-12/IL-23p40, IL-17A, MCP-1, TNF-α) and anti-inflammatory cytokines (IL-4, IL-10) were measured. Twenty-eight-day mortality, %TBSA, prognostic burn index (PBI) and SOFA and APACHE II scores were evaluated. Hierarchical clustering analysis and network visualization showed one cluster and network, respectively. Both were formed by four cytokines including IL-6, IL-8, IL-10 and MCP-1 on days 1 and 2, suggesting the presence of a cytokine network in the early hospital phase. Each cytokine showed significant associations with the SOFA score within 5 days and 1 month after burn injury. Cox regression analysis highlighting days 1 and 2 showed significant correlation of IL-6, IL-8 and IL-10 with 28-day mortality. We showed a cytokine network and its relation with prognosis and injury severity on days 1 and 2 and suggest that this cytokine network may play a role in major burns.