How the innate and adaptive host immune system miscommunicate to worsen COVID-19 immunopathology has not been fully elucidated. Here, we perform single-cell deep-immune profiling of bronchoalveolar lavage (BAL) samples from 5 patients with mild and 26 with critical COVID-19 in comparison to BALs from non-COVID-19 pneumonia and normal lung. We use pseudotime inference to build T-cell and monocyte-to-macrophage trajectories and model gene expression changes along them. In mild COVID-19, CD8+ resident-memory (TRM) and CD4+ T-helper-17 (TH17) cells undergo active (presumably antigen-driven) expansion towards the end of the trajectory, and are characterized by good effector functions, while in critical COVID-19 they remain more naive. Vice versa, CD4+ T-cells with T-helper-1 characteristics (TH1-like) and CD8+ T-cells expressing exhaustion markers (TEX-like) are enriched halfway their trajectories in mild COVID-19, where they also exhibit good effector functions, while in critical COVID-19 they show evidence of inflammation-associated stress at the end of their trajectories. Monocyte-to-macrophage trajectories show that chronic hyperinflammatory monocytes are enriched in critical COVID-19, while alveolar macrophages, otherwise characterized by anti-inflammatory and antigen-presenting characteristics, are depleted. In critical COVID-19, monocytes contribute to an ATP-purinergic signaling-inflammasome footprint that could enable COVID-19 associated fibrosis and worsen disease-severity. Finally, viral RNA-tracking reveals infected lung epithelial cells, and a significant proportion of neutrophils and macrophages that are involved in viral clearance.

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Discriminating mild from critical COVID-19 by innate and adaptive immune single-cell profiling of bronchoalveolar lavages.

https://doi.org/10.1016/j.intimp.2021.108516

Neutrophil Extracellular Traps (NETs) and Covid-19: A new frontiers for therapeutic modality

The extreme diversity of the human immune system, forged and maintained throughout evolutionary history, provides a potent defense against opportunistic pathogens. At the same time, this immune variation is the substrate upon which a plethora of immune-associated diseases develop. Genetic analysis suggests that thousands of individually weak loci together drive up to half of the observed immune variation. Intense selection maintains this genetic diversity, even selecting for the introgressed Neanderthal or Denisovan alleles that have reintroduced variation lost during the out-of-Africa migration. Variations in age, sex, diet, environmental exposure, and microbiome each potentially explain the residual variation, with proof-of-concept studies demonstrating both plausible mechanisms and correlative associations. The confounding interaction of many of these variables currently makes it difficult to assign definitive contributions. Here, we review the current state of play in the field, identify the key unknowns in the causality of immune variation, and identify the multidisciplinary pathways toward an improved understanding.

Human immune diversity: from evolution to modernity.

Impaired response to first SARS-CoV-2 dose vaccination in myeloproliferative neoplasm patients receiving ruxolitinib.

Objectives Emerging evidence of dysregulation of the myeloid cell compartment urges investigations on neutrophil characteristics in coronavirus disease 2019 (COVID-19). We isolated neutrophils from the blood of COVID-19 patients receiving general ward care and from patients hospitalised at intensive care units (ICUs) to explore the kinetics of circulating neutrophils and factors important for neutrophil migration and activation. Methods Multicolour flow cytometry was exploited for the analysis of neutrophil differentiation and activation markers. Multiplex and ELISA technologies were used for the quantification of protease, protease inhibitor, chemokine and cytokine concentrations in plasma. Neutrophil polarisation responses were evaluated microscopically. Gelatinolytic and metalloproteinase activity in plasma was determined using a fluorogenic substrate. Co-culturing healthy donor neutrophils with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) allowed us to investigate viral replication in neutrophils. Results Upon ICU admission, patients displayed high plasma concentrations of granulocyte-colony-stimulating factor (G-CSF) and the chemokine CXCL8, accompanied by emergency myelopoiesis as illustrated by high levels of circulating CD10-, immature neutrophils with reduced CXCR2 and C5aR expression. Neutrophil elastase and non-metalloproteinase-derived gelatinolytic activity were increased in plasma from ICU patients. Significantly higher levels of circulating tissue inhibitor of metalloproteinase 1 (TIMP-1) in patients at ICU admission yielded decreased total MMP proteolytic activity in blood. COVID-19 neutrophils were hyper-responsive to CXCL8 and CXCL12 in shape change assays. Finally, SARS-CoV-2 failed to replicate inside human neutrophils. Conclusion Our study provides detailed insights into the kinetics of neutrophil phenotype and function in severe COVID-19 patients, and supports the concept of an increased neutrophil activation state in the circulation.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/cti2.1271

Kinetics of peripheral blood neutrophils in severe coronavirus disease 2019.

Epidemiological and clinical reports indicate that SARS-CoV-2 virulence hinges upon the triggering of an aberrant host immune response, more so than on direct virus-induced cellular damage. To elucidate the immunopathology underlying COVID-19 severity, we perform cytokine and multiplex immune profiling in COVID-19 patients. We show that hypercytokinemia in COVID-19 differs from the interferon-gamma-driven cytokine storm in macrophage activation syndrome, and is more pronounced in critical versus mild-moderate COVID-19. Systems modelling of cytokine levels paired with deep-immune profiling shows that classical monocytes drive this hyper-inflammatory phenotype and that a reduction in T-lymphocytes correlates with disease severity, with CD8+ cells being disproportionately affected. Antigen presenting machinery expression is also reduced in critical disease. Furthermore, we report that neutrophils contribute to disease severity and local tissue damage by amplification of hypercytokinemia and the formation of neutrophil extracellular traps. Together our findings suggest a myeloid-driven immunopathology, in which hyperactivated neutrophils and an ineffective adaptive immune system act as mediators of COVID-19 disease severity.

https://biblio.ugent.be/publication/8717259/file/8717260.pdf

Monocyte-driven atypical cytokine storm and aberrant neutrophil activation as key mediators of COVID-19 disease severity.

The host immune response in symptomatic COVID-19 patients seems ineffective in clearing SARS-CoV-2, yet excessive in causing local tissue damage and hypercytokinemia. To elucidate the immunopathology underlying COVID-19 severity, cytokine profiling was performed in mild-moderate and critically-ill COVID-19 patients. Hypercytokinemia in COVID-19 differed from the IFN-γ-driven cytokine storm in macrophage activation syndrome, but was increased in critical versus mild-moderate COVID-19. Systems modelling of cytokine levels followed by deep-immune profiling showed that classical monocytes drive this hyper-inflammatory phenotype and that both a quantitative and qualitative reduction in T-lymphocytes correlate with disease severity, with CD8+ cells being disproportionately affected. Expression of antigen presentation and co-stimulatory molecules was reduced in critical disease, while also neutrophils contributed to disease severity and local tissue damage by amplifying hypercytokinemia and neutrophil extracellular trap formation. We suggest a monocyte-driven immunopathology, in which hyperactivated neutrophils and an ineffective adaptive immune system act as mediators of COVID-19 disease severity.

Funding: This work was funded by KU Leuven (internal fund and grant C14/17/084 and C16/17/010), VIB (Grand Challenge project), UZ Leuven (KOOR project), FWO grant I007418N, the Rega Foundation (research expert fellowship to G.M.) and ‘het Leuvens Kankerinstituut’. E.D. is a postdoctoral research fellow of the Research Foundation – Flanders (FWO), Belgium (grant number 12X9420N). J.G. holds a postdoctoral research fellowship granted by the clinical research and education council of the University Hospitals Leuven. Y.S. received funding from the Flemish Government (AI Research Program). L.V. is supported by an FWO PhD fellowship (grant number 11E9819N). P.V.M. is supported by an FWO PhD fellowship (grant number 1S66020N). S.V.G. is an ISAC Marylou Ingram Scholar and supported by an FWO postdoctoral research grant (Research Foundation – Flanders). E.W. is supported by Stichting tegen Kanker (Mandate for basic & clinical oncology research). J.W. is supported by an FWO Fundamental Clinical Mandate (1833317N). 

Conflict of Interest: The authors declare no competing interests.

Ethical Approval: All study procedures were approved by the Ethics Committee of the University Hospitals Leuven. Informed consent was obtained from all individuals or their legal guardians.

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R. Vos

Papers

Monocyte-driven atypical cytokine storm and aberrant neutrophil activation as key mediators of COVID-19 disease severity.

Monocyte-Driven Atypical Cytokine Storm and Aberrant Neutrophil Activation as Key Mediators of COVID19 Disease Severity