Phenotypic alteration of low-density granulocytes in people with pulmonary post-acute sequalae of SARS-CoV-2 infection

Interferon-α Inhibits NET Formation in Neutrophils Derived from Patients with Myeloproliferative Neoplasms in a Neutrophil Sub-Population-Specific Manner

Neutrophils and neutrophil extracellular traps (NETs) contribute to thrombosis and hyperinflammation in myeloproliferative neoplasms (MPN). High-density neutrophils (HDNs) and low-density neutrophils (LDNs) have recently been characterized as distinct neutrophil sub-populations with distinct morphological and functional properties. We aim to study the kinetics of NET formation and inhibition with interferon-α (IFNα) in neutrophils derived from patients with MPN as compared to matched healthy controls. Ex vivo NET formation was assessed by neutrophil-elastase activity, neutrophil-associated nucleosomes, myeloperoxidase (MPO), and citrullinated histone H3 content. IFNα significantly inhibited NET formation in neutrophils derived from MPN patients. Neutrophil sub-population analysis demonstrated that HDNs drive the increase in NET formation as compared to LDNs in patients and in healthy controls and are effectively inhibited by IFNα, an effect that is lost in LDNs. In conclusion, we demonstrate that in MPN, HDNs drive excess NET formation and are more sensitive to IFNα inhibition. These observations uncover unique neutrophil sub-population biology and dynamics in MPN.

Long COVID syndrome in children: neutrophilic granulocyte dysfunction and its correlation with disease severity

BACKGROUND

Many children suffer from lingering symptoms after COVID-19, known as long COVID syndrome (LCS), otherwise called Post COVID-19 Condition (PCC). Despite extensive research, the prevalence of symptoms, its impact on quality of life, and underlying mechanisms still need to be fully understood. As neutrophilic granulocytes play an essential role in COVID-19, and their prolonged disruption was found to cause immunological diseases, we hypothesized their ongoing disturbed functionality in LCS.

METHODS

We studied 129 children with LCS, 32 convalescent children (CG+), and 8 uninfected children (CG-). Online questionnaires and in-person examinations assessed symptoms, quality of life, and functioning (QoL-F). Effector functions of neutrophilic granulocytes obtained from the venous blood of 29 LCS and 17 CG+ children were also investigated.

RESULTS

Persistent fatigue was the most common symptom in children with LCS, while both control groups complained about anxiety most frequently. LCS children experienced significantly more symptoms, impairing their QoL-F compared to CG+. Neutrophilic granulocyte dysfunction was found in LCS children, with decreased superoxide-producing activity and phagocytosis compared to CG+. The number of complaints of children with LCS correlated significantly with altered neutrophil effector functions.

CONCLUSION

Neutrophil dysfunction in children with LCS may be part of the disease pathogenesis or a predisposing factor.

IMPACT

Using online questionnaires validated during in-person medical examinations and including two different control groups, our study compellingly supports and adds to previous clinical observations in the field. Our study provides valuable insights into the prevalence and characteristics of pediatric LCS, highlighting the significant quality of life and functioning impairment compared to control groups. By detecting neutrophilic granulocyte dysfunction in children with LCS, we shed light on a previously overlooked pathophysiological component of the condition. We demonstrate a significant correlation between clinical symptoms and superoxide production, further enhancing our understanding of the underlying mechanisms of pediatric LCS.

Novel Clinical, Immunological, and Metabolic Features Associated with Persistent Post-Acute COVID-19 Syndrome

The coronavirus disease 2019 (COVID-19) survivors are frequently observed to present persistent symptoms constituting what has been called "post-acute COVID-19 syndrome" (PACS) or "long COVID-19". Some clinical risk factors have been identified to be associated with PACS development; however, specific mechanisms responsible for PACS pathology remain unknown. This study investigates clinical, immunological, and metabolomic risk factors associated with post-acute COVID-19 syndrome (PACS) in 51 patients, assessed 7-19 months after acute infection. Among the participants, 62.7% were male and 37.2% were female, with an average age of 47.8 years. At the follow-up, 37.2% met the criteria for PACS, revealing significant differences in immunological and metabolomic profiles at the time of acute infection. Patients with PACS were characterized by elevated levels of mature low-density granulocytes (LDGs), interleukin-8 (IL-8), pyruvate, pseudouridine, and cystine. Baseline multivariate analysis showed increased pyruvate and decreased alpha tocopherol levels. At follow-up, there was a decrease in absolute B lymphocytes and an increase in non-classical monocytes and 3-hydroxyisovaleric acid levels. These findings suggest that specific immunological and metabolomic markers during acute infection can help identify patients at higher risk of developing persistent PACS.

Inflammation-, immunothrombosis,- and autoimmune-feedback loops may lead to persistent neutrophil self-stimulation in long COVID

Understanding the pathophysiology of long COVID is one of the most intriguing challenges confronting contemporary medicine. Despite observations recently made in the relevant molecular, cellular, and physiological domains, it is still difficult to say whether the post-acute sequelae of COVID-19 directly correspond to the consequences of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. This work hypothesizes that neutrophils and neutrophil extracellular traps (NETs) production are at the interconnection of three positive feedback loops which are initiated in the acute phase of SARS-CoV-2 infection, and which involve inflammation, immunothrombosis, and autoimmunity. This phenomenon could be favored by the fact that SARS-CoV-2 may directly bind and penetrate neutrophils. The ensuing strong neutrophil stimulation leads to a progressive amplification of an exacerbated and uncontrolled NETs production, potentially persisting for months beyond the acute phase of infection. This continuous self-stimulation of neutrophils leads, in turn, to systemic inflammation, micro-thromboses, and the production of autoantibodies, whose significant consequences include the persistence of endothelial and multiorgan damage, and vascular complications.

CPHEN-017: Comprehensive phenotyping of neutrophil extracellular traps (NETs) on peripheral human neutrophils

With the recent discovery of their ability to produce neutrophil extracellular traps (NETs), neutrophils are increasingly appreciated as active participants in infection and inflammation. NETs are characterized as large, web-like networks of DNA and proteins extruded from neutrophils, and there is considerable interest in how these structures drive disease in humans. Advancing research in this field is contingent on developing novel tools for quantifying NETosis. To this end, we have developed a 7-marker flow cytometry panel for analyzing NETosis on human peripheral neutrophils following in vitro stimulation, and in fresh circulating neutrophils under inflammatory conditions. This panel was optimized on neutrophils isolated from whole blood and analyzed fresh or in vitro stimulated with phorbol 12-myristate 13-acetate (PMA) or ionomycin, two known NET-inducing agonists. Neutrophils were identified as SSChighFSChighCD15+CD66b+. Neutrophils positive for amine residues and 7-Aminoactinomycin D (7-AAD), our DNA dye of choice, were deemed necrotic (Zombie-NIR+7-AAD+) and were removed from downstream analysis. Exclusion of Zombie-NIR and positivity for 7-AAD (Zombie-NIRdim7-AAD+) was used here as a marker of neutrophil-appendant DNA, a key feature of NETs. The presence of two NET-associated proteins - myeloperoxidase (MPO) and neutrophil elastase (NE) - were utilized to identify neutrophil-appendant NET events (SSChighFSChighCD15+CD66b+Zombie NIRdim7-AAD+MPO+NE+). We also demonstrate that NETotic neutrophils express citrullinated histone H3 (H3cit), are concentration-dependently induced by in vitro PMA and ionomycin stimulation but are disassembled with DNase treatment, and are present in both chronic and acute inflammation. This 7-color flow cytometry panel provides a novel tool for examining NETosis in humans.

Immunology of SARS-CoV-2 Infection

According to the data from the World Health Organization, about 800 million of the world population had contracted coronavirus infection caused by SARS-CoV-2 by mid-2023. Properties of this virus have allowed it to circulate in the human population for a long time, evolving defense mechanisms against the host immune system. Severity of the disease depends largely on the degree of activation of the systemic immune response, including overstimulation of macrophages and monocytes, cytokine production, and triggering of adaptive T- and B-cell responses, while SARS-CoV-2 evades the immune system actions. In this review, we discuss immune responses triggered in response to the SARS-CoV-2 virus entry into the cell and malfunctions of the immune system that lead to the development of severe disease.

Thromboinflammation in long COVID-the elusive key to postinfection sequelae?

Long COVID is a public health emergency affecting millions of people worldwide, characterized by heterogeneous symptoms across multiple organ systems. Here, we discuss the current evidence linking thromboinflammation to postacute sequelae of COVID-19. Studies have found persistence of vascular damage with increased circulating markers of endothelial dysfunction, coagulation abnormalities with heightened thrombin generation capacity, and abnormalities in platelet counts in postacute sequelae of COVID-19. Neutrophil phenotype resembles acute COVID-19 with an increase in activation and Neutrophil Extracellular Trap formation. These insights are potentially linked by elevated platelet-neutrophil aggregate formation. This hypercoagulable state in turn can lead to microvascular thrombosis, evidenced by microclots and elevated D-dimer in the circulation as well as perfusion abnormalities in the lungs and brains of patients with long COVID. Also, COVID-19 survivors experience an increased rate of arterial and venous thrombotic events. We discuss 3 important, potentially intertwined hypotheses that might contribute to thromboinflammation in long COVID: lasting structural changes, most prominently endothelial damage, caused during initial infection; a persistent viral reservoir; and immunopathology driven by a misguided immune system. Finally, we outline the necessity for large, well-characterized clinical cohorts and mechanistic studies to clarify the contribution of thromboinflammation to long COVID.