Persistent NLRP3 inflammasome activation is associated with delayed immunosuppression in septic patients

Sepsis triggers a complex response marked by the simultaneous presence of proinflammatory and immunosuppressive elements, disrupting the mechanisms intended to maintain homeostasis. While the NLRP3 inflammasome has been demonstrated to contribute to the inflammatory side, its connection with delayed sepsis-induced immunosuppression remains unexplored. The present objective was to concomitantly and prospectively assess NLRP3 activation (IL-1β, IL-18, and soluble receptors) and features of immune failure (IL-10, mHLA-DR, myeloid-derived suppressor cells) in septic patients. To validate our findings, we conducted a transcriptomic analysis of mRNA of NLRP3-related genes (IL-18R1, IL-1R2) on an additional cohort of 107 patients. Two distinct endotypes were identified. One cluster displayed moderate inflammation rapidly returning to normal values, while the other exhibited a higher inflammatory response persisting until day 28, which was associated with persistent marked immunosuppression and higher 28-d mortality. Identifying endotypes with different pro/anti-inflammatory trajectories could hold important clinical implications for the management of sepsis.

Altered Ex Vivo NLRP3 Inflammasome Activation Is Associated with 28-Day Mortality in Septic Patients

Sepsis is a life-threatening organ dysfunction caused by a dysregulated response to infection. In this context, the aberrant activation of the NLRP3 inflammasome has been documented mostly through the measurement of increased plasmatic concentrations of IL-1β and IL-18. At the cellular level, contradictory results have been published. However, no study has comprehensively monitored NLRP3 inflammasome activation at the basal level and after ex vivo reactivation of whole blood monocytes and neutrophils focusing on ICU patients with bacterial and viral sepsis, including a longitudinal analysis. Thus, we conducted a prospective longitudinal study, examining NLRP3 inflammasome functionality in COVID-19 ICU patients (n = 15) and bacterial septic shock patients (n = 17) during the first week of ICU hospitalization, compared with healthy donors. Using two whole-blood flow cytometry assays, we detected ASC speck-positive monocytes (i.e., monocytes presenting the polymerization of ASC proteins) and activated caspase-1 in polymorphonuclear cells as read-outs, both at baseline and following nigericin stimulation, a drug that forms pores and activates the NLRP3 inflammasome. Our findings showed that, at baseline and regardless of the type of infection, patients exhibited reduced ASC speck-positive monocytes and decreased activated caspase-1 in PMN compared to healthy volunteers. This decrease was prominent at day 0. Following nigericin stimulation, this reduction was also observed and persisted throughout the first week of hospitalization, irrespective of the cellular population or parameter being considered. Notably, at day 0, this diminished activation and response to stimulation of NLRP3 was associated with a higher 28-day mortality rate. Consequently, our observations highlighted a concurrent decline in both basal expression and ex vivo activation of the NLRP3 inflammasome in circulating myeloid cells from patients with bacterial and viral sepsis in association with increased mortality.

Assessment of neutrophil subsets and immune checkpoint inhibitor expressions on T lymphocytes in liver transplantation: A preliminary study beyond the neutrophil-lymphocyte ratio

Background: Advanced stages of cirrhosis are characterized by the occurrence of progressive immune alterations known as CAID (Cirrhosis Associated Immune Dysfunction). In advanced cirrhosis, liver transplantation (LT) remains the only curative treatment. Sepsis, shares many similarities with decompensated cirrhosis in terms of immuno-inflammatory response. In both conditions, the neutrophil-lymphocyte ratio (NLR) is associated with poor outcomes. Based on alterations in sepsis, we hypothesized that we could observe in cirrhotic and LT patients more detailed neutrophil and lymphocyte phenotypes. To this end, along with leukocyte count, we assessed immature neutrophils, LOX-1⁺ MDSC and PD-1 and TIM-3 lymphocyte expressions in cirrhotic patients before transplantation in association with liver disease severity and during the first month after transplantation. Methods: We conducted a prospective monocentric study including cirrhotic patients registered on LT waiting-list. Blood samples were collected at enrolment before LT and for 1 month post-LT. In addition to NLR, we assessed by whole blood flow cytometry the absolute count of immature neutrophils and LOX-1⁺ MDSC as well as the expressions of immune checkpoint receptors PD-1 and TIM-3 on T lymphocytes. Results: We included 15 healthy volunteers (HV) and 28 patients. LT was performed for 13 patients. Pre-LT patients presented with a higher NLR compared to HV and NLR was associated with cirrhosis severity. Increased immature neutrophils and LOX-1⁺ MDSC counts were observed in the most severe patients. These alterations were mainly associated with acute decompensation of cirrhosis. PD-1 and TIM-3 expressions on T lymphocytes were not different between patients and HV. Post-LT immune alterations were dominated by a transitory but tremendous increase of NLR and immature neutrophils during the first days post-LT. Then, immune checkpoint receptors and LOX-1⁺ MDSC tended to be overexpressed by the second week after surgery. Conclusion: The present study showed that NLR, immature neutrophils and LOX-1⁺ MDSC counts along with T lymphocyte count and checkpoint inhibitor expression were altered in cirrhotic patients before and after LT. These data illustrate the potential interest of immune monitoring of cirrhotic patients in the context of LT in order to better define risk of sepsis. For this purpose, larger cohorts of patients are now necessary in order to move forward a more personalised care of LT patients.

[Role of inflammasome NLRP3 in the pathophysiology of viral infections: A focus on SARS-CoV-2 infection]

NLRP3 is one of the best characterized innate immune cytosolic sensor. As part of the innate immune response, the NLRP3 inflammasome detects a wide range of danger signals such as pathogens, tissue damages, cellular stress. The priming and activation of NLRP3 lead to the formation of an oligomeric intracellular complex and to the recruitment and activation of caspase-1. Once activated, not only this inflammasome complex controls the processing and release of pro-inflammatory factors including IL-1β and IL-18, but also the inflammatory cell death pyroptosis mediated by gasdermin D pores. In this review, we describe the role of the NLRP3 inflammasome activation in viral infections with a particular interest on SARS-CoV-2 infection. In addition, we present therapies evaluated or under evaluation targeting the NLRP3 inflammasome pathway as COVID-19 treatment.

T cell response against SARS-CoV-2 persists after one year in patients surviving severe COVID-19

BACKGROUND

In critically ill COVID-19 patients, the initial response to SARS-CoV-2 infection is characterized by major immune dysfunctions. The capacity of these severe patients to mount a robust and persistent SARS-CoV-2 specific T cell response despite the presence of severe immune alterations during the ICU stay is unknown.

METHODS

Critically ill COVID-19 patients were sampled five times during the ICU stay and 9 and 13 months afterwards. Immune monitoring included counts of lymphocyte subpopulations, HLA-DR expression on monocytes, plasma IL-6 and IL-10 concentrations, anti-SARS-CoV-2 IgG levels and T cell proliferation in response to three SARS-CoV-2 antigens.

FINDINGS

Despite the presence of major lymphopenia and decreased monocyte HLA-DR expression during the ICU stay, convalescent critically ill COVID-19 patients consistently generated adaptive and humoral immune responses against SARS-CoV-2 maintained for more than one year after hospital discharge. Patients with long hospital stays presented with stronger anti-SARS-CoV-2 specific T cell response but no difference in anti-SARS-CoV2 IgG levels.

INTERPRETATION

Convalescent critically ill COVID-19 patients consistently generated a memory immune response against SARS-CoV-2 maintained for more than one year after hospital discharge. In recovered individuals, the intensity of SARS-CoV-2 specific T cell response was dependent on length of hospital stay.

FUNDING

This observational study was supported by funds from the Hospices Civils de Lyon, Fondation HCL, Claude Bernard Lyon 1 University and Région Auvergne Rhône-Alpes and by partial funding by REACTing (Research and ACTion targeting emerging infectious diseases) INSERM, France and a donation from Fondation AnBer (http://fondationanber.fr/).

Emergence of immunosuppressive LOX-1+ PMN-MDSC in septic shock and severe COVID-19 patients with acute respiratory distress syndrome

Myeloid‐derived suppressor cells (MDSC) are a heterogeneous population of immature myeloid cells with immunosuppressive properties. In cancer patients, the expression of lectin‐type oxidized LDL receptor 1 (LOX‐1) on granulocytic MDSC identifies a subset of MDSC that retains the most potent immunosuppressive properties. The main objective of the present work was to explore the presence of LOX‐1+ MDSC in bacterial and viral sepsis. To this end, whole blood LOX‐1+ cells were phenotypically, morphologically, and functionally characterized. They were monitored in 39 coronavirus disease‐19 (COVID‐19, viral sepsis) and 48 septic shock (bacterial sepsis) patients longitudinally sampled five times over a 3 wk period in intensive care units (ICUs). The phenotype, morphology, and immunosuppressive functions of LOX‐1+ cells demonstrated that they were polymorphonuclear MDSC. In patients, we observed the significant emergence of LOX‐1+ MDSC in both groups. The peak of LOX‐1+ MDSC was 1 wk delayed with respect to ICU admission. In COVID‐19, their elevation was more pronounced in patients with acute respiratory distress syndrome. The persistence of these cells may contribute to long lasting immunosuppression leaving the patient unable to efficiently resolve infections.

Characterization of Circulating IL-10-Producing Cells in Septic Shock Patients: A Proof of Concept Study

Sepsis is a worldwide health priority characterized by the occurrence of severe immunosuppression associated with increased risk of death and secondary infections. Interleukin 10 (IL-10) is a potent immunosuppressive cytokine which plasma concentration is increased in septic patients in association with deleterious outcomes. Despite studies evaluating IL-10 production in specific subpopulations of purified cells, the concomitant description of IL-10 production in monocytes and lymphocytes in septic patients' whole blood has never been performed. In this pilot study, we characterized IL-10 producing leukocytes in septic shock patients through whole blood intracellular staining by flow cytometry. Twelve adult septic shock patients and 9 healthy volunteers were included. Intracellular tumor necrosis factor-α (TNFα) and IL-10 productions after lipopolysaccharide stimulation by monocytes and IL-10 production after PMA/Ionomycine stimulation by lymphocytes were evaluated. Standard immunomonitoring (HLA-DR expression on monocytes, CD4+ T lymphocyte count) of patients was also performed. TNFα expression by stimulated monocytes was reduced in patients compared with controls while IL-10 production was increased. This was correlated with a reduced monocyte HLA-DR expression. B cells, CD4+, and CD4- T lymphocytes were the three circulating IL-10 producing lymphocyte subsets in both patients and controls. No difference in IL-10 production between patients and controls was observed for B and CD4- T cells. However, IL-10 production by CD4+ T lymphocytes significantly increased in patients in parallel with reduced CD4+ T cells number. Parameters reflecting altered monocyte (increased IL-10 production, decreased HLA-DR expression and decreased TNFα synthesis) and CD4+ T lymphocyte (increased IL-10 production, decreased circulating number) responses were correlated. Using a novel technique for intracellular cytokine measurement in whole blood, our results identify monocytes and CD4+ T cells as the main IL-10 producers in septic patients' whole blood and illustrate the development of a global immunosuppressive profile in septic shock. Overall, these preliminary results add to our understanding of the global increase in IL-10 production induced by septic shock. Further research is mandatory to determine the pathophysiological mechanisms leading to such increased IL-10 production in monocytes and CD4+ T cells.

Monocyte HLA-DR Measurement by Flow Cytometry in COVID-19 Patients: An Interim Review

Several months after the sudden emergence of SARS-CoV-2 and COVID-19, the understanding of the appropriate host immune response to a virus totally unknown of human immune surveillance is still of major importance. By international definition, COVID-19 falls in the scope of septic syndromes (organ dysfunction due to dysregulated host response to an infection) in which immunosuppression is a significant driver of mortality. Sepsis-induced immunosuppression is mostly defined and monitored by the measurement of decreased expression of HLA-DR molecules on circulating monocytes (mHLA-DR). In this interim review, we summarize the first mHLA-DR results in COVID-19 patients. In critically ill patients, results homogenously indicate a decreased mHLA-DR expression, which, along with profound lymphopenia and other functional alterations, is indicative of a status of immunosuppression. © 2020 International Society for Advancement of Cytometry.