A persistent neutrophil-associated immune signature characterizes post-COVID-19 pulmonary sequelae

Recognition and control of neutrophil extracellular trap formation by MICL

Regulation of neutrophil activation is critical for disease control. Neutrophil extracellular traps (NETs), which are web-like structures composed of DNA and neutrophil-derived proteins, are formed following pro-inflammatory signals; however, if this process is uncontrolled, NETs contribute to disease pathogenesis, exacerbating inflammation and host tissue damage1,2. Here we show that myeloid inhibitory C-type lectin-like (MICL), an inhibitory C-type lectin receptor, directly recognizes DNA in NETs; this interaction is vital to regulate neutrophil activation. Loss or inhibition of MICL functionality leads to uncontrolled NET formation through the ROS-PAD4 pathway and the development of an auto-inflammatory feedback loop. We show that in the context of rheumatoid arthritis, such dysregulation leads to exacerbated pathology in both mouse models and in human patients, where autoantibodies to MICL inhibit key functions of this receptor. Of note, we also detect similarly inhibitory anti-MICL autoantibodies in patients with other diseases linked to aberrant NET formation, including lupus and severe COVID-19. By contrast, dysregulation of NET release is protective during systemic infection with the fungal pathogen Aspergillus fumigatus. Together, we show that the recognition of NETs by MICL represents a fundamental autoregulatory pathway that controls neutrophil activity and NET formation.

Post-COVID pulmonary injury in K18-hACE2 mice shows persistent neutrophils and neutrophil extracellular trap formation

The involvement of neutrophils in the lungs during the recovery phase of coronavirus disease 2019 (COVID-19) is not well defined mainly due to the limited accessibility of lung tissues from COVID-19 survivors. The lack of an appropriate small animal model has affected the development of effective therapeutic strategies. We here developed a long COVID mouse model to study changes in neutrophil phenotype and association with lung injury. Our data shows persistent neutrophil recruitment and neutrophil extracellular trap formation in the lungs for up to 30 days post-infection which correlates with lung fibrosis and inflammation.

Neutrophil extracellular traps promote immunopathogenesis of virus-induced COPD exacerbations

Respiratory viruses are a major trigger of exacerbations in chronic obstructive pulmonary disease (COPD). Airway neutrophilia is a hallmark feature of stable and exacerbated COPD but roles played by neutrophil extracellular traps (NETS) in driving disease pathogenesis are unclear. Here, using human studies of experimentally-induced and naturally-occurring exacerbations we identify that rhinovirus infection induces airway NET formation which is amplified in COPD and correlates with magnitude of inflammation and clinical exacerbation severity. We show that inhibiting NETosis protects mice from immunopathology in a model of virus-exacerbated COPD. NETs drive inflammation during exacerbations through release of double stranded DNA (dsDNA) and administration of DNAse in mice has similar protective effects. Thus, NETosis, through release of dsDNA, has a functional role in the pathogenesis of COPD exacerbations. These studies open up the potential for therapeutic targeting of NETs or dsDNA as a strategy for treating virus-exacerbated COPD.

Proteomic analysis of lung responses to SARS-CoV-2 infection in aged non-human primates: clinical and research relevance

With devastating health and socioeconomic impact worldwide, much work is left to understand the Coronavirus Disease 2019 (COVID-19), with emphasis in the severely affected elderly population. Here, we present a proteomics study of lung tissue obtained from aged vs. young rhesus macaques (Macaca mulatta) and olive baboons (Papio Anubis) infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Using age as a variable, we identified common proteomic profiles in the lungs of aged infected non-human primates (NHPs), including key regulators of immune function, as well as cell and tissue remodeling, and discuss the potential clinical relevance of such parameters. Further, we identified key differences in proteomic profiles between both NHP species, and compared those to what is known about SARS-CoV-2 in humans. Finally, we explored the translatability of these animal models in the context of aging and the human presentation of the COVID-19.

Single-cell analysis of bronchoalveolar cells in inflammatory and fibrotic post-COVID lung disease

Background

Persistent radiological lung abnormalities are evident in many survivors of acute coronavirus disease 2019 (COVID-19). Consolidation and ground glass opacities are interpreted to indicate subacute inflammation whereas reticulation is thought to reflect fibrosis. We sought to identify differences at molecular and cellular level, in the local immunopathology of post-COVID inflammation and fibrosis.

Methods

We compared single-cell transcriptomic profiles and T cell receptor (TCR) repertoires of bronchoalveolar cells obtained from convalescent individuals with each radiological pattern, targeting lung segments affected by the predominant abnormality.

Results

CD4 central memory T cells and CD8 effector memory T cells were significantly more abundant in those with inflammatory radiology. Clustering of similar TCRs from multiple donors was a striking feature of both phenotypes, consistent with tissue localised antigen-specific immune responses. There was no enrichment for known SARS-CoV-2-reactive TCRs, raising the possibility of T cell-mediated immunopathology driven by failure in immune self-tolerance.

Conclusions

Post-COVID radiological inflammation and fibrosis show evidence of shared antigen-specific T cell responses, suggesting a role for therapies targeting T cells in limiting post-COVID lung damage.

Characteristics and determinants of pulmonary long COVID

BACKGROUNDPersistent cough and dyspnea are prominent features of postacute sequelae of SARS-CoV-2 (also termed "long COVID"); however, physiologic measures and clinical features associated with these pulmonary symptoms remain poorly defined. Using longitudinal pulmonary function testing (PFT) and CT imaging, this study aimed to identify the characteristics and determinants of pulmonary long COVID.METHODSThis single-center retrospective study included 1,097 patients with clinically defined long COVID characterized by persistent pulmonary symptoms (dyspnea, cough, and chest discomfort) lasting for 1 or more months after resolution of primary COVID infection.RESULTSAfter exclusion, a total of 929 patients with post-COVID pulmonary symptoms and PFTs were stratified as diffusion impairment and pulmonary restriction, as measured by percentage predicted diffusion capacity for carbon monoxide (DLCO) and total lung capacity (TLC). Longitudinal evaluation revealed diffusion impairment (DLCO ≤ 80%) and pulmonary restriction (TLC ≤ 80%) in 51% of the cohort overall (n = 479). In multivariable modeling regression analysis, invasive mechanical ventilation during primary infection conferred the greatest increased odds of developing pulmonary long COVID with diffusion impairment and restriction (adjusted odds ratio [aOR] = 9.89, 95% CI 3.62-26.9]). Finally, a subanalysis of CT imaging identified radiographic evidence of fibrosis in this patient population.CONCLUSIONLongitudinal PFTs revealed persistent diffusion-impaired restriction as a key feature of pulmonary long COVID. These results emphasize the importance of incorporating PFTs into routine clinical practice for evaluation of long COVID patients with prolonged pulmonary symptoms. Subsequent clinical trials should leverage combined symptomatic and quantitative PFT measurements for more targeted enrollment of pulmonary long COVID patients.FUNDINGNational Institute of Allergy and Infectious Diseases (AI156898, K08AI129705), National Heart, Lung, and Blood Institute (HL153113, OTA21-015E, HL149944), and the COVID-19 Urgent Research Response Fund at the University of Alabama at Birmingham.

Plasma-Free Blood as a Potential Alternative to Whole Blood for Transcriptomic Analysis

RNA sequencing (RNAseq) technology has become increasingly important in precision medicine and clinical diagnostics, and emerged as a powerful tool for identifying protein-coding genes, performing differential gene analysis, and inferring immune cell composition. Human peripheral blood samples are widely used for RNAseq, providing valuable insights into individual biomolecular information. Blood samples can be classified as whole blood (WB), plasma, serum, and remaining sediment samples, including plasma-free blood (PFB) and serum-free blood (SFB) samples that are generally considered less useful byproducts during the processes of plasma and serum separation, respectively. However, the feasibility of using PFB and SFB samples for transcriptome analysis remains unclear. In this study, we aimed to assess the suitability of employing PFB or SFB samples as an alternative RNA source in transcriptomic analysis. We performed a comparative analysis of WB, PFB, and SFB samples for different applications. Our results revealed that PFB samples exhibit greater similarity to WB samples than SFB samples in terms of protein-coding gene expression patterns, detection of differentially expressed genes, and immunological characterizations, suggesting that PFB can serve as a viable alternative to WB for transcriptomic analysis. Our study contributes to the optimization of blood sample utilization and the advancement of precision medicine research.

Supplementary Information

The online version contains supplementary material available at 10.1007/s43657-023-00121-1.

Small Molecules for the Treatment of Long-COVID-Related Vascular Damage and Abnormal Blood Clotting: A Patent-Based Appraisal

People affected by COVID-19 are exposed to, among others, abnormal clotting and endothelial dysfunction, which may result in deep vein thrombosis, cerebrovascular disorders, and ischemic and non-ischemic heart diseases, to mention a few. Treatments for COVID-19 include antiplatelet (e.g., aspirin, clopidogrel) and anticoagulant agents, but their impact on morbidity and mortality has not been proven. In addition, due to viremia-associated interconnected prothrombotic and proinflammatory events, anti-inflammatory drugs have also been investigated for their ability to mitigate against immune dysregulation due to the cytokine storm. By retrieving patent literature published in the last two years, small molecules patented for long-COVID-related blood clotting and hematological complications are herein examined, along with supporting evidence from preclinical and clinical studies. An overview of the main features and therapeutic potentials of small molecules is provided for the thromboxane receptor antagonist ramatroban, the pan-caspase inhibitor emricasan, and the sodium-hydrogen antiporter 1 (NHE-1) inhibitor rimeporide, as well as natural polyphenolic compounds.

Systems analysis of innate and adaptive immunity in Long COVID

Since the onset of the COVID-19 pandemic, significant progress has been made in developing effective preventive and therapeutic strategies against severe acute SARS-CoV-2 infection. However, the management of Long COVID (LC), an infection-associated chronic condition that has been estimated to affect 5-20% of individuals following SARS-CoV-2 infection, remains challenging due to our limited understanding of its mechanisms. Although LC is a heterogeneous disease that is likely to have several subtypes, immune system disturbances appear common across many cases. The extent to which these immune perturbations contribute to LC symptoms, however, is not entirely clear. Recent advancements in multi-omics technologies, capable of detailed, cell-level analysis, have provided valuable insights into the immune perturbations associated with LC. Although these studies are largely descriptive in nature, they are the crucial first step towards a deeper understanding of the condition and the immune system's role in its development, progression, and resolution. In this review, we summarize the current understanding of immune perturbations in LC, covering both innate and adaptive immune responses, and the cytokines and analytes involved. We explore whether these findings support or challenge the primary hypotheses about LC's underlying mechanisms. We also discuss the crosstalk between various immune system components and how it can be disrupted in LC. Finally, we emphasize the need for more tissue- and subtype-focused analyses of LC, and for enhanced collaborative efforts to analyze common specimens from large cohorts, including those undergoing therapeutic interventions. These collective efforts are vital to unravel the fundaments of this new disease, and could also shed light on the prevention and treatment of the larger family of chronic illnesses linked to other microbial infections.

Cardiovascular dysautonomia in postacute sequelae of SARS-CoV-2 infection

Coronavirus disease 2019 (COVID-19) has led to a worldwide pandemic that continues to transform but will not go away. Cardiovascular dysautonomia in postacute sequelae of severe acute respiratory syndrome coronavirus 2 infection has led to persistent symptoms in a large number of patients. Here, we define the condition and its associated symptoms as well as potential mechanisms responsible. We provide a careful and complete overview of the topic addressing novel studies and a generalized approach to the management of individuals with this complex and potentially debilitating problem. We also discuss future research directions and the important knowledge gaps to be addressed in ongoing and planned studies.

Extensive acute and sustained changes to neutrophil proteomes post-SARS-CoV-2 infection

BACKGROUND

Neutrophils are important in the pathophysiology of coronavirus disease 2019 (COVID-19), but the molecular changes contributing to altered neutrophil phenotypes following severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection are not fully understood. We used quantitative mass spectrometry-based proteomics to explore neutrophil phenotypes immediately following acute SARS-CoV-2 infection and during recovery.

METHODS

Prospective observational study of hospitalised patients with PCR-confirmed SARS-CoV-2 infection (May to December 2020). Patients were enrolled within 96 h of admission, with longitudinal sampling up to 29 days. Control groups comprised non-COVID-19 acute lower respiratory tract infection (LRTI) and age-matched noninfected controls. Neutrophils were isolated from peripheral blood and analysed using mass spectrometry. COVID-19 severity and recovery were defined using the World Health Organization ordinal scale.

RESULTS

Neutrophil proteomes from 84 COVID-19 patients were compared to those from 91 LRTI and 42 control participants. 5800 neutrophil proteins were identified, with >1700 proteins significantly changed in neutrophils from COVID-19 patients compared to noninfected controls. Neutrophils from COVID-19 patients initially all demonstrated a strong interferon signature, but this signature rapidly declined in patients with severe disease. Severe disease was associated with increased abundance of proteins involved in metabolism, immunosuppression and pattern recognition, while delayed recovery from COVID-19 was associated with decreased granule components and reduced abundance of metabolic proteins, chemokine and leukotriene receptors, integrins and inhibitory receptors.

CONCLUSIONS

SARS-CoV-2 infection results in the sustained presence of circulating neutrophils with distinct proteomes suggesting altered metabolic and immunosuppressive profiles and altered capacities to respond to migratory signals and cues from other immune cells, pathogens or cytokines.

Neutrophil Extracellular Traps Upregulate p21 and Suppress Cell Cycle Progression to Impair Endothelial Regeneration after Inflammatory Lung Injury

Background: Sepsis is a major cause of ICU admissions, with high mortality and morbidity. The lungs are particularly vulnerable to infection and injury, and restoration of vascular endothelial homeostasis after injury is a crucial determinant of outcome. Neutrophil extracellular trap (NET) release strongly correlates with the severity of lung tissue damage. However, little is known about whether NETs affect endothelial cell (EC) regeneration and repair. Methods: Eight- to ten-week-old male C57BL/6 mice were injected intraperitoneally with a sublethal dose of LPS to induce acute lung inflammatory injury or with PBS as a control. Blood samples and lung tissues were collected to detect NET formation and lung endothelial cell proliferation. Human umbilical vein endothelial cells (HUVECs) were used to determine the role of NETs in cell cycle progression in vitro. Results: Increased NET formation and impaired endothelial cell proliferation were observed in mice with inflammatory lung injury following septic endotoxemia. Degradation of NETs with DNase I attenuated lung inflammation and facilitated endothelial regeneration. Mechanistically, NETs induced p21 upregulation and cell cycle stasis to impair endothelial repair. Conclusions: Our findings suggest that NET formation impairs endothelial regeneration and vascular repair through the induction of p21 and cell cycle arrest during inflammatory lung injury.

MicroRNA-guided drug discovery for mitigating persistent pulmonary complications in critical COVID-19 survivors: A longitudinal pilot study

BACKGROUND AND PURPOSE

The post-acute sequelae of SARS-CoV-2 infection pose a significant global challenge, with nearly 50% of critical COVID-19 survivors manifesting persistent lung abnormalities. The lack of understanding about the molecular mechanisms and effective treatments hampers their management. Here, we employed microRNA (miRNA) profiling to decipher the systemic molecular underpinnings of the persistent pulmonary complications.

EXPERIMENTAL APPROACH

We conducted a longitudinal investigation including 119 critical COVID-19 survivors. A comprehensive pulmonary evaluation was performed in the short-term (median = 94.0 days after hospital discharge) and long-term (median = 358 days after hospital discharge). Plasma miRNAs were quantified at the short-term evaluation using the gold-standard technique, RT-qPCR. The analyses combined machine learning feature selection techniques with bioinformatic investigations. Two additional datasets were incorporated for validation.

KEY RESULTS

In the short-term, 84% of the survivors exhibited impaired lung diffusion (DLCO  < 80% of predicted). One year post-discharge, 54.4% of this patient subgroup still presented abnormal DLCO . Four feature selection methods identified two specific miRNAs, miR-9-5p and miR-486-5p, linked to persistent lung dysfunction. The downstream experimentally validated targetome included 1473 genes, with heterogeneous enriched pathways associated with inflammation, angiogenesis and cell senescence. Validation studies using RNA-sequencing and proteomic datasets emphasized the pivotal roles of cell migration and tissue repair in persistent lung dysfunction. The repositioning potential of the miRNA targets was limited.

CONCLUSION AND IMPLICATIONS

Our study reveals early mechanistic pathways contributing to persistent lung dysfunction in critical COVID-19 survivors, offering a promising approach for the development of targeted disease-modifying agents.

Characteristics and Determinants of Pulmonary Long COVID

RATIONALE

Persistent cough and dyspnea are prominent features of post-acute sequelae of SARS-CoV-2 (termed 'Long COVID'); however, physiologic measures and clinical features associated with these pulmonary symptoms remain poorly defined.

OBJECTIVES

Using longitudinal pulmonary function testing (PFTs) and CT imaging, this study aimed to identify the characteristics and determinants of pulmonary Long COVID.

METHODS

The University of Alabama at Birmingham Pulmonary Long COVID cohort was utilized to characterize lung defects in patients with persistent pulmonary symptoms after resolution primary COVID infection. Longitudinal PFTs including total lung capacity (TLC) and diffusion limitation of carbon monoxide (DLCO) were used to evaluate restriction and diffusion impairment over time in this cohort. Analysis of chest CT imaging was used to phenotype the pulmonary Long COVID pathology. Risk factors linked to development of pulmonary Long COVID were estimated using univariate and multivariate logistic regression models.

MEASUREMENTS AND MAIN RESULTS

Longitudinal evaluation 929 patients with post-COVID pulmonary symptoms revealed diffusion impairment (DLCO ≤80%) and restriction (TLC ≤80%) in 51% of the cohort (n=479). In multivariable logistic regression analysis (adjusted odds ratio; aOR, 95% confidence interval [CI]), invasive mechanical ventilation during primary infection conferred the greatest increased odds of developing pulmonary Long COVID with diffusion impaired restriction (aOR=10.9 [4.09-28.6]). Finally, a sub-analysis of CT imaging identified evidence of fibrosis in this population.

CONCLUSIONS

Persistent diffusion impaired restriction was identified as a key feature of pulmonary Long COVID. Subsequent clinical trials should leverage combined symptomatic and quantitative PFT measurements for more targeted enrollment of pulmonary Long COVID patients.

Autoimmunity and long COVID in children

Numerous hypotheses regarding the pathogenetic mechanisms of long COVID have been proposed. Immune dysregulation and autoimmunity are among the leading hypotheses. In this article, we present two clinical cases of long COVID. The first case demonstrates the phenotype of long COVID with pain and musculoskeletal symptoms, which is often associated with autoimmunity and mimics systemic connective tissue diseases. In the second case, a high titer of antinuclear antibodies was observed after SARS-CoV-2 infection, but the clinical symptoms were limited to fever and headache. Only a comprehensive evaluation of clinical symptoms and thorough objective examination can confirm or exclude autoimmune diseases after a previous SARS-CoV-2 infection. A systematic search in the PubMed Medline database was carried out for studies focusing on immune dysregulation, autoimmunity, and its association with the clinical phenotype of long COVID. The question of the role of autoimmunity in the development of long COVID and the management approaches are discussed.

High-dimensional comparison of monocytes and T cells in post-COVID and idiopathic pulmonary fibrosis

Introduction

Up to 30% of hospitalized COVID-19 patients experience persistent sequelae, including pulmonary fibrosis (PF).

Methods

We examined COVID-19 survivors with impaired lung function and imaging worrisome for developing PF and found within six months, symptoms, restriction and PF improved in some (Early-Resolving COVID-PF), but persisted in others (Late-Resolving COVID-PF). To evaluate immune mechanisms associated with recovery versus persistent PF, we performed single-cell RNA-sequencing and multiplex immunostaining on peripheral blood mononuclear cells from patients with Early- and Late-Resolving COVID-PF and compared them to age-matched controls without respiratory disease.

Results and discussion

Our analysis showed circulating monocytes were significantly reduced in Late-Resolving COVID-PF patients compared to Early-Resolving COVID-PF and non-diseased controls. Monocyte abundance correlated with pulmonary function forced vital capacity and diffusion capacity. Differential expression analysis revealed MHC-II class molecules were upregulated on the CD8 T cells of Late-Resolving COVID-PF patients but downregulated in monocytes. To determine whether these immune signatures resembled other interstitial lung diseases, we analyzed samples from Idiopathic Pulmonary Fibrosis (IPF) patients. IPF patients had a similar marked decrease in monocyte HLA-DR protein expression compared to Late-Resolving COVID-PF patients. Our findings indicate decreased circulating monocytes are associated with decreased lung function and uniquely distinguish Late-Resolving COVID-PF from Early-Resolving COVID-PF, IPF, and non-diseased controls.

Long COVID: Molecular Mechanisms and Detection Techniques

Long COVID, also known as post-acute sequelae of SARS-CoV-2 infection (PASC), has emerged as a significant health concern following the COVID-19 pandemic. Molecular mechanisms underlying the occurrence and progression of long COVID include viral persistence, immune dysregulation, endothelial dysfunction, and neurological involvement, and highlight the need for further research to develop targeted therapies for this condition. While a clearer picture of the clinical symptomatology is shaping, many molecular mechanisms are yet to be unraveled, given their complexity and high level of interaction with other metabolic pathways. This review summarizes some of the most important symptoms and associated molecular mechanisms that occur in long COVID, as well as the most relevant molecular techniques that can be used in understanding the viral pathogen, its affinity towards the host, and the possible outcomes of host-pathogen interaction.

Beyond the Acute Phase: Long-Term Impact of COVID-19 on Functional Capacity and Prothrombotic Risk-A Pilot Study

Background and Objectives: Assessment of the prothrombotic, proinflammatory, and functional status of a cohort of COVID-19 patients at least two years after the acute infection to identify parameters with potential therapeutic and prognostic value. Materials and Methods: We conducted a retrospective, descriptive study that included 117 consecutive patients admitted to Iasi Pulmonary Rehabilitation Clinic for reassessment and a rehabilitation program at least two years after a COVID-19 infection. The cohort was divided into two groups based on the presence (n = 49) or absence (n = 68) of pulmonary fibrosis, documented through high-resolution computer tomography. Results: The cohort comprises 117 patients, 69.23% females, with a mean age of 65.74 ± 10.19 years and abnormal body mass index (31.42 ± 5.71 kg/m2). Patients with pulmonary fibrosis have significantly higher levels of C-reactive protein (CRP) (p < 0.05), WBC (7.45 ± 7.86/mm3 vs. 9.18 ± 17.24/mm3, p = 0.053), neutrophils (4.68 ± 7.88/mm3 vs. 9.07 ± 17.44/mm3, p < 0.05), mean platelet volume (MPV) (7.22 ± 0.93 vs. 10.25 ± 0.86 fL, p < 0.05), lactate dehydrogenase (p < 0.05), and D-dimers (p < 0.05), but not ferritin (p = 0.470), reflecting the chronic proinflammatory and prothrombotic status. Additionally, patients with associated pulmonary fibrosis had a higher mean heart rate (p < 0.05) and corrected QT interval (p < 0.05). D-dimers were strongly and negatively correlated with diffusion capacity corrected for hemoglobin (DLCO corr), and ROC analysis showed that the persistence of high D-dimers values is a predictor for low DLCO values (ROC analysis: area under the curve of 0.772, p < 0.001). The results of pulmonary function tests (spirometry, body plethysmography) and the 6-minute walk test demonstrated no significant difference between groups, without notable impairment within either group. Conclusions: Patients with COVID-19-related pulmonary fibrosis have a persistent long-term proinflammatory, prothrombotic status, despite the functional recovery. The persistence of elevated D-dimer levels could emerge as a predictive factor associated with impaired DLCO.

MAFB shapes human monocyte-derived macrophage response to SARS-CoV-2 and controls severe COVID-19 biomarker expression

Monocyte-derived macrophages, the major source of pathogenic macrophages in COVID-19, are oppositely instructed by macrophage CSF (M-CSF) or granulocyte macrophage CSF (GM-CSF), which promote the generation of antiinflammatory/immunosuppressive MAFB+ (M-MØ) or proinflammatory macrophages (GM-MØ), respectively. The transcriptional profile of prevailing macrophage subsets in severe COVID-19 led us to hypothesize that MAFB shapes the transcriptome of pulmonary macrophages driving severe COVID-19 pathogenesis. We have now assessed the role of MAFB in the response of monocyte-derived macrophages to SARS-CoV-2 through genetic and pharmacological approaches, and we demonstrate that MAFB regulated the expression of the genes that define pulmonary pathogenic macrophages in severe COVID-19. Indeed, SARS-CoV-2 potentiated the expression of MAFB and MAFB-regulated genes in M-MØ and GM-MØ, where MAFB upregulated the expression of profibrotic and neutrophil-attracting factors. Thus, MAFB determines the transcriptome and functions of the monocyte-derived macrophage subsets that underlie pulmonary pathogenesis in severe COVID-19 and controls the expression of potentially useful biomarkers for COVID-19 severity.

Fungal microbiota sustains lasting immune activation of neutrophils and their progenitors in severe COVID-19

Gastrointestinal fungal dysbiosis is a hallmark of several diseases marked by systemic immune activation. Whether persistent pathobiont colonization during immune alterations and impaired gut barrier function has a durable impact on host immunity is unknown. We found that elevated levels of Candida albicans immunoglobulin G (IgG) antibodies marked patients with severe COVID-19 (sCOVID-19) who had intestinal Candida overgrowth, mycobiota dysbiosis and systemic neutrophilia. Analysis of hematopoietic stem cell progenitors in sCOVID-19 revealed transcriptional changes in antifungal immunity pathways and reprogramming of granulocyte myeloid progenitors (GMPs) for up to a year. Mice colonized with C. albicans patient isolates experienced increased lung neutrophilia and pulmonary NETosis during severe acute respiratory syndrome coronavirus-2 infection, which were partially resolved with antifungal treatment or by interleukin-6 receptor blockade. sCOVID-19 patients treated with tocilizumab experienced sustained reductions in C. albicans IgG antibodies titers and GMP transcriptional changes. These findings suggest that gut fungal pathobionts may contribute to immune activation during inflammatory diseases, offering potential mycobiota-immune therapeutic strategies for sCOVID-19 with prolonged symptoms.

Persistent endothelial dysfunction in post-COVID-19 syndrome and its associations with symptom severity and chronic inflammation

BACKGROUND

Post-COVID-19 syndrome (PCS) is a lingering disease with ongoing symptoms such as fatigue and cognitive impairment resulting in a high impact on the daily life of patients. Understanding the pathophysiology of PCS is a public health priority, as it still poses a diagnostic and treatment challenge for physicians.

METHODS

In this prospective observational cohort study, we analyzed the retinal microcirculation using Retinal Vessel Analysis (RVA) in a cohort of patients with PCS and compared it to an age- and gender-matched healthy cohort (n = 41, matched out of n = 204).

MEASUREMENTS AND MAIN RESULTS

PCS patients exhibit persistent endothelial dysfunction (ED), as indicated by significantly lower venular flicker-induced dilation (vFID; 3.42% ± 1.77% vs. 4.64% ± 2.59%; p = 0.02), narrower central retinal artery equivalent (CRAE; 178.1 [167.5-190.2] vs. 189.1 [179.4-197.2], p = 0.01) and lower arteriolar-venular ratio (AVR; (0.84 [0.8-0.9] vs. 0.88 [0.8-0.9], p = 0.007). When combining AVR and vFID, predicted scores reached good ability to discriminate groups (area under the curve: 0.75). Higher PCS severity scores correlated with lower AVR (R = - 0.37 p = 0.017). The association of microvascular changes with PCS severity were amplified in PCS patients exhibiting higher levels of inflammatory parameters.

CONCLUSION

Our results demonstrate that prolonged endothelial dysfunction is a hallmark of PCS, and impairments of the microcirculation seem to explain ongoing symptoms in patients. As potential therapies for PCS emerge, RVA parameters may become relevant as clinical biomarkers for diagnosis and therapy management.

TRIAL REGISTRATION

This study was previously registered at ClinicalTrials ("All Eyes on PCS-Analysis of the Retinal Microvasculature in Patients with Post-COVID-19 Syndrome". NCT05635552. https://clinicaltrials.gov/ct2/show/NCT05635552 ). Persistent endothelial dysfunction in post-COVID-19 syndrome. Acute SARS-CoV-2 infection indirectly or directly causes endotheliitis in patients. N = 41 PCS patients were recruited and retinal vessel analysis was performed to assess microvascular endothelial function. Images of SVA and DVA are illustrative for RVA data analysis. For each PCS patient and healthy cohort, venular vessel diameter of the three measurement cycles was calculated and plotted on a diameter-time curve. Patients exhibited reduced flicker-induced dilation in veins (vFID) measured by dynamic vessel analysis (DVA) and lower central retinal arteriolar equivalent (CRAE) and arteriolar-venular ratio (AVR) and a tendency towards higher central retinal venular equivalent (CRVE) when compared to SARS-CoV-2 infection naïve participants. Created with BioRender.com.

Neutrophil extracellular traps and long COVID

Post-acute COVID-19 sequelae, commonly known as long COVID, encompasses a range of systemic symptoms experienced by a significant number of COVID-19 survivors. The underlying pathophysiology of long COVID has become a topic of intense research discussion. While chronic inflammation in long COVID has received considerable attention, the role of neutrophils, which are the most abundant of all immune cells and primary responders to inflammation, has been unfortunately overlooked, perhaps due to their short lifespan. In this review, we discuss the emerging role of neutrophil extracellular traps (NETs) in the persistent inflammatory response observed in long COVID patients. We present early evidence linking the persistence of NETs to pulmonary fibrosis, cardiovascular abnormalities, and neurological dysfunction in long COVID. Several uncertainties require investigation in future studies. These include the mechanisms by which SARS-CoV-2 brings about sustained neutrophil activation phenotypes after infection resolution; whether the heterogeneity of neutrophils seen in acute SARS-CoV-2 infection persists into the chronic phase; whether the presence of autoantibodies in long COVID can induce NETs and protect them from degradation; whether NETs exert differential, organ-specific effects; specifically which NET components contribute to organ-specific pathologies, such as pulmonary fibrosis; and whether senescent cells can drive NET formation through their pro-inflammatory secretome in long COVID. Answering these questions may pave the way for the development of clinically applicable strategies targeting NETs, providing relief for this emerging health crisis.

Atopy and Elevation of IgE, IgG3, and IgG4 May Be Risk Factors for Post COVID-19 Condition in Children and Adolescents

SARS-CoV-2 infection causes transient cardiorespiratory and neurological disorders, and severe acute illness is rare among children. Post COVID-19 condition (PCC) may cause profound, persistent phenotypes with increasing prevalence. Its manifestation and risk factors remain elusive. In this monocentric study, we hypothesized that atopy, the tendency to produce an exaggerated immunoglobulin E (IgE) immune response, is a risk factor for the manifestation of pediatric PCC. We present a patient cohort (n = 28) from an early pandemic period (2021-2022) with comprehensive evaluations of phenotypes, pulmonary function, and molecular investigations. PCC predominantly affected adolescents and presented with fatigue, dyspnea, and post-exertional malaise. Sensitizations to aeroallergens were found in 93% of cases. We observed elevated IgE levels (mean 174.2 kU/L, reference < 100 kU/L) regardless of disease severity. Concurrent Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) was found in 29% of patients that also faced challenges in school attendance. ME/CFS manifestation was significantly associated with elevated immunoglobulin G subclasses IgG3 (p < 0.05) and IgG4 (p < 0.05). A total of 57% of patients showed self-limiting disease courses with mean recovery at 12.7 months (range 5-25 months), 29% at 19.2 months (range 12-30 months), and the rest demonstrated overall improvement. These findings offer additional insights into immune dysregulation as a risk factor for pediatric PCC.

Exploring the Immune Response against RSV and SARS-CoV-2 Infection in Children

Viral respiratory tract infections are a significant public health concern, particularly in children. RSV is a prominent cause of lower respiratory tract infections among infants, whereas SARS-CoV-2 has caused a global pandemic with lower overall severity in children than in adults. In this review, we aimed to compare the innate and adaptive immune responses induced by RSV and SARS-CoV-2 to better understand differences in the pathogenesis of infection. Some studies have demonstrated that children present a more robust immune response against SARS-CoV-2 than adults; however, this response is dissimilar to that of RSV. Each virus has a distinctive mechanism to escape the immune response. Understanding the mechanisms underlying these differences is crucial for developing effective treatments and improving the management of pediatric respiratory infections.

Respiratory sequelae of COVID-19: pulmonary and extrapulmonary origins, and approaches to clinical care and rehabilitation

Although the exact prevalence of post-COVID-19 condition (also known as long COVID) is unknown, more than a third of patients with COVID-19 develop symptoms that persist for more than 3 months after SARS-CoV-2 infection. These sequelae are highly heterogeneous in nature and adversely affect multiple biological systems, although breathlessness is a frequently cited symptom. Specific pulmonary sequelae, including pulmonary fibrosis and thromboembolic disease, need careful assessment and might require particular investigations and treatments. COVID-19 outcomes in people with pre-existing respiratory conditions vary according to the nature and severity of the respiratory disease and how well it is controlled. Extrapulmonary complications such as reduced exercise tolerance and frailty might contribute to breathlessness in post-COVID-19 condition. Non-pharmacological therapeutic options, including adapted pulmonary rehabilitation programmes and physiotherapy techniques for breathing management, might help to attenuate breathlessness in people with post-COVID-19 condition. Further research is needed to understand the origins and course of respiratory symptoms and to develop effective therapeutic and rehabilitative strategies.

Systems analysis of human innate immunity in COVID-19

Recent developments in sequencing technologies, the computer and data sciences, as well as increasingly high-throughput immunological measurements have made it possible to derive holistic views on pathophysiological processes of disease and treatment effects directly in humans. We and others have illustrated that incredibly predictive data for immune cell function can be generated by single cell multi-omics (SCMO) technologies and that these technologies are perfectly suited to dissect pathophysiological processes in a new disease such as COVID-19, triggered by SARS-CoV-2 infection. Systems level interrogation not only revealed the different disease endotypes, highlighted the differential dynamics in context of disease severity, and pointed towards global immune deviation across the different arms of the immune system, but was already instrumental to better define long COVID phenotypes, suggest promising biomarkers for disease and therapy outcome predictions and explains treatment responses for the widely used corticosteroids. As we identified SCMO to be the most informative technologies in the vest to better understand COVID-19, we propose to routinely include such single cell level analysis in all future clinical trials and cohorts addressing diseases with an immunological component.

Persistent immune and clotting dysfunction detected in saliva and blood plasma after COVID-19

A growing number of studies indicate that coronavirus disease 2019 (COVID-19) is associated with inflammatory sequelae, but molecular signatures governing the normal versus pathologic convalescence process have not been well-delineated. Here, we characterized global immune and proteome responses in matched plasma and saliva samples obtained from COVID-19 patients collected between 20 and 90 days after initial clinical symptoms resolved. Convalescent subjects showed robust total IgA and IgG responses and positive antibody correlations in saliva and plasma samples. Shotgun proteomics revealed persistent inflammatory patterns in convalescent samples including dysfunction of salivary innate immune cells, such as neutrophil markers (e.g., myeloperoxidase), and clotting factors in plasma (e.g., fibrinogen), with positive correlations to acute COVID-19 disease severity. Saliva samples were characterized by higher concentrations of IgA, and proteomics showed altered myeloid-derived pathways that correlated positively with SARS-CoV-2 IgA levels. Beyond plasma, our study positions saliva as a viable fluid to monitor normal and aberrant immune responses including vascular, inflammatory, and coagulation-related sequelae.

Tissue-resident memory T cells and lung immunopathology

Rapid reaction to microbes invading mucosal tissues is key to protect the host against disease. Respiratory tissue-resident memory T (TRM ) cells provide superior immunity against pathogen infection and/or re-infection, due to their presence at the site of pathogen entry. However, there has been emerging evidence that exuberant TRM -cell responses contribute to the development of various chronic respiratory conditions including pulmonary sequelae post-acute viral infections. In this review, we have described the characteristics of respiratory TRM cells and processes underlying their development and maintenance. We have reviewed TRM -cell protective functions against various respiratory pathogens as well as their pathological activities in chronic lung conditions including post-viral pulmonary sequelae. Furthermore, we have discussed potential mechanisms regulating the pathological activity of TRM cells and proposed therapeutic strategies to alleviate TRM -cell-mediated lung immunopathology. We hope that this review provides insights toward the development of future vaccines or interventions that can harness the superior protective abilities of TRM cells, while minimizing the potential for immunopathology, a particularly important topic in the era of coronavirus disease 2019 (COVID-19) pandemic.

Myeloperoxidase inhibition may protect against endothelial glycocalyx shedding induced by COVID-19 plasma

BACKGROUND

SARS-CoV-2, the causative agent of COVID-19, is a threat to public health. Evidence suggests increased neutrophil activation and endothelial glycocalyx (EG) damage are independently associated with severe COVID-19. Here, we hypothesised that an increased level of blood neutrophil myeloperoxidase (MPO) is associated with soluble EG breakdown, and inhibiting MPO activity may reduce EG damage.

METHODS

Analysing a subset of acute and convalescent COVID-19 plasma, 10 from severe and 15 from non-severe COVID-19 cases, and 9 from pre-COVID-19 controls, we determined MPO levels, MPO activity and soluble EG proteins (syndecan-1 and glypican-1) levels by enzyme-linked immunosorbent assay. In vitro primary human aortic endothelial cells were cultured with plasma untreated or treated with specific MPO inhibitors (MPO-IN-28, AZD5904) to determine EG shedding. We then investigated whether inhibiting MPO activity decreased EG degradation.

RESULTS

In COVID-19 plasma, MPO levels, MPO activity and levels of soluble EG proteins are significantly raised compared to controls, and concentrations increase in proportion to disease severity. Despite clinical recovery, protein concentrations remain significantly elevated. Interestingly, there is a trend of increasing MPO activity in convalescent plasma in both severe and non-severe groups. MPO levels and MPO activity correlate significantly with soluble EG levels and inhibiting MPO activity leads to reduced syndecan-1 shedding, in vitro.

CONCLUSIONS

Neutrophil MPO may increase EG shedding in COVID-19, and inhibiting MPO activity may protect against EG degradation. Further research is needed to evaluate the utility of MPO inhibitors as potential therapeutics against severe COVID-19.

SARS-CoV-2 infection results in upregulation of Plasminogen Activator Inhibitor-1 and Neuroserpin in the lungs, and an increase in fibrinolysis inhibitors associated with disease severity

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection results in coagulation activation although it is usually not associated with consumption coagulopathy. D-dimers are also commonly elevated despite systemic hypofibrinolysis. To understand these unusual features of coronavirus disease 2019 (COVID-19) coagulopathy, 64 adult patients with SARS-CoV-2 infection (36 moderate and 28 severe) and 16 controls were studied. We evaluated the repertoire of plasma protease inhibitors (Serpins, Kunitz, Kazal, Cystatin-like) targeting the fibrinolytic system: Plasminogen Activator Inhibitor-1 (PAI-1), Tissue Plasminogen Activator/Plasminogen Activator Inhibitor-1 complex (t-PA/PAI-1), α-2-Antiplasmin, Plasmin-α2-Antiplasmin Complex, Thrombin-activatable Fibrinolysis Inhibitor (TAFI)/TAFIa, Protease Nexin-1 (PN-1), and Neuroserpin (the main t-PA inhibitor of the central nervous system). Inhibitors of the common (Antithrombin, Thrombin-antithrombin complex, Protein Z [PZ]/PZ inhibitor, Heparin Cofactor II, and α2-Macroglobulin), Protein C ([PC], Protein C inhibitor, and Protein S), contact (Kallistatin, Protease Nexin-2/Amyloid Beta Precursor Protein, and α-1-Antitrypsin), and complement (C1-Inhibitor) pathways, in addition to Factor XIII, Histidine-rich glycoprotein (HRG) and Vaspin were also investigated by enzyme-linked immunosorbent assay. The association of these markers with disease severity was evaluated by logistic regression. Pulmonary expression of PAI-1 and Neuroserpin in the lungs from eight post-mortem cases was assessed by immunohistochemistry. Results show that six patients (10%) developed thrombotic events, and mortality was 11%. There was no significant reduction in plasma anticoagulants, in keeping with a compensated state. However, an increase in fibrinolysis inhibitors (PAI-1, Neuroserpin, PN-1, PAP, and t-PA/PAI-1) was consistently observed, while HRG was reduced. Furthermore, these markers were associated with moderate and/or severe disease. Notably, immunostains demonstrated overexpression of PAI-1 in epithelial cells, macrophages, and endothelial cells of fatal COVID-19, while Neuroserpin was found in intraalveolar macrophages only. These results imply that the lungs in SARS-CoV-2 infection provide anti-fibrinolytic activity resulting in a shift toward a local and systemic hypofibrinolytic state predisposing to (immuno)thrombosis, often in a background of compensated disseminated intravascular coagulation.

Long COVID: Clinical characteristics, proposed pathogenesis and potential therapeutic targets

The emergence of persistent ill-health in the aftermath of SARS-CoV-2 infection has presented significant challenges to patients, healthcare workers and researchers. Termed long COVID, or post-acute sequelae of COVID-19 (PASC), the symptoms of this condition are highly variable and span multiple body systems. The underlying pathophysiology remains poorly understood, with no therapeutic agents proven to be effective. This narrative review describes predominant clinical features and phenotypes of long COVID alongside the data supporting potential pathogenesis of these phenotypes including ongoing immune dysregulation, viral persistence, endotheliopathy, gastrointestinal microbiome disturbance, autoimmunity, and dysautonomia. Finally, we describe current potential therapies under investigation, as well as future potential therapeutic options based on the proposed pathogenesis research.

A Brief Overview of Neutrophils in Neurological Diseases

Neutrophils are the most abundant leukocyte in circulation and are the first line of defense after an infection or injury. Neutrophils have a broad spectrum of functions, including phagocytosis of microorganisms, the release of pro-inflammatory cytokines and chemokines, oxidative burst, and the formation of neutrophil extracellular traps. Traditionally, neutrophils were thought to be most important for acute inflammatory responses, with a short half-life and a more static response to infections and injury. However, this view has changed in recent years showing neutrophil heterogeneity and dynamics, indicating a much more regulated and flexible response. Here we will discuss the role of neutrophils in aging and neurological disorders; specifically, we focus on recent data indicating the impact of neutrophils in chronic inflammatory processes and their contribution to neurological diseases. Lastly, we aim to conclude that reactive neutrophils directly contribute to increased vascular inflammation and age-related diseases.

Inflammation and Epstein-Barr Virus at the Crossroads of Multiple Sclerosis and Post-Acute Sequelae of COVID-19 Infection

Recent studies have strengthened the evidence for Epstein-Barr Virus (EBV) as an important contributing factor in the development of multiple sclerosis (MS). Chronic inflammation is a key feature of MS. EBV+ B cells can express cytokines and exosomes that promote inflammation, and EBV is known to be reactivated through the upregulation of cellular inflammasomes. Inflammation is a possible cause of the breakdown of the blood-brain barrier (BBB), which allows the infiltration of lymphocytes into the central nervous system. Once resident, EBV+ or EBV-specific B cells could both plausibly exacerbate MS plaques through continued inflammatory processes, EBV reactivation, T cell exhaustion, and/or molecular mimicry. Another virus, SARS-CoV-2, the cause of COVID-19, is known to elicit a strong inflammatory response in infected and immune cells. COVID-19 is also associated with EBV reactivation, particularly in severely ill patients. Following viral clearance, continued inflammation may be a contributor to post-acute sequelae of COVID-19 infection (PASC). Evidence of aberrant cytokine activation in patients with PASC supports this hypothesis. If unaddressed, long-term inflammation could put patients at risk for reactivation of EBV. Determining mechanisms by which viruses can cause inflammation and finding treatments for reducing that inflammation may help reduce the disease burden for patients suffering from PASC, MS, and EBV diseases.

Emergence and antibody evasion of BQ, BA.2.75 and SARS-CoV-2 recombinant sub-lineages in the face of maturing antibody breadth at the population level

BACKGROUND

The Omicron era of the COVID-19 pandemic commenced at the beginning of 2022 and whilst it started with primarily BA.1, it was latter dominated by BA.2 and the related sub-lineage BA.5. Following resolution of the global BA.5 wave, a diverse grouping of Omicron sub-lineages emerged derived from BA.2, BA.5 and recombinants thereof. Whilst emerging from distinct lineages, all shared similar changes in the Spike glycoprotein affording them an outgrowth advantage through evasion of neutralising antibodies.

METHODS

Over the course of 2022, we monitored the potency and breadth of antibody neutralization responses to many emerging variants in the Australian community at three levels: (i) we tracked over 420,000 U.S. plasma donors over time through various vaccine booster roll outs and Omicron waves using sequentially collected IgG pools; (ii) we mapped the antibody response in individuals using blood from stringently curated vaccine and convalescent cohorts. (iii) finally we determine the in vitro efficacy of clinically approved therapies Evusheld and Sotrovimab.

FINDINGS

In pooled IgG samples, we observed the maturation of neutralization breadth to Omicron variants over time through continuing vaccine and infection waves. Importantly, in many cases, we observed increased antibody breadth to variants that were yet to be in circulation. Determination of viral neutralization at the cohort level supported equivalent coverage across prior and emerging variants with isolates BQ.1.1, XBB.1, BR.2.1 and XBF the most evasive. Further, these emerging variants were resistant to Evusheld, whilst increasing neutralization resistance to Sotrovimab was restricted to BQ.1.1 and XBF. We conclude at this current point in time that dominant variants can evade antibodies at levels equivalent to their most evasive lineage counterparts but sustain an entry phenotype that continues to promote an additional outgrowth advantage. In Australia, BR.2.1 and XBF share this phenotype and, in contrast to global variants, are uniquely dominant in this region in the later months of 2022.

INTERPRETATION

Whilst the appearance of a diverse range of omicron lineages has led to primary or partial resistance to clinically approved monoclonal antibodies, the maturation of the antibody response across both cohorts and a large donor pools importantly observes increasing breadth in the antibody neutralisation responses over time with a trajectory that covers both current and known emerging variants.

FUNDING

This work was primarily supported by Australian Medical Foundation research grants MRF2005760 (SGT, GM & WDR), Medical Research Future Fund Antiviral Development Call grant (WDR), the New South Wales Health COVID-19 Research Grants Round 2 (SGT & FB) and the NSW Vaccine Infection and Immunology Collaborative (VIIM) (ALC). Variant modeling was supported by funding from SciLifeLab's Pandemic Laboratory Preparedness program to B.M. (VC-2022-0028) and by the European Union's Horizon 2020 research and innovation programme under grant agreement no. 101003653 (CoroNAb) to B.M.

Down-regulation of KLF2 in lung fibroblasts is linked with COVID-19 immunofibrosis and restored by combined inhibition of NETs, JAK-1/2 and IL-6 signaling

Kruppel-like factor 2 (KLF2) has been linked with fibrosis and neutrophil-associated thromboinflammation; however, its role in COVID-19 remains elusive. We investigated the effect of disease microenvironment on the fibrotic potential of human lung fibroblasts (LFs) and its association with KLF2 expression. LFs stimulated with plasma from severe COVID-19 patients down-regulated KLF2 expression at mRNA/protein and functional level acquiring a pre-fibrotic phenotype, as indicated by increased CCN2/collagen levels. Pre-incubation with the COMBI-treatment-agents (DNase I and JAKs/IL-6 inhibitors baricitinib/tocilizumab) restored KLF2 levels of LFs to normal abolishing their fibrotic activity. LFs stimulated with plasma from COMBI-treated patients at day-7 expressed lower CCN2 and higher KLF2 levels, compared to plasma prior-to-treatment, an effect not observed in standard-of-care treatment. In line with this, COMBI-treated patients had better outcome than standard-of-care group. These data link fibroblast KLF2 with NETosis and JAK/IL-6 signaling, suggesting the potential of combined therapeutic strategies in immunofibrotic diseases, such as COVID-19.

Microvascular Thrombosis as a Critical Factor in Severe COVID-19

Platelet-endothelial interactions have a critical role in microcirculatory function, which maintains tissue homeostasis. The subtle equilibrium between platelets and the vessel wall is disturbed by the coronavirus disease 2019 (COVID-19), which affects all three components of Virchow's triad (endothelial injury, stasis and a hypercoagulable state). Endotheliitis, vasculitis, glycocalyx degradation, alterations in blood flow and viscosity, neutrophil extracellular trap formation and microparticle shedding are only few pathomechanisms contributing to endothelial damage and microthrombosis resulting in capillary plugging and tissue ischemia. In the following opinion paper, we discuss major pathological processes leading to microvascular endothelial activation and thrombosis formation as a possible major adverse factor driving the deterioration of patient disease course in severe COVID-19.

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

Background

Low-density granulocytes (LDGs) are a distinct subset of neutrophils whose increased abundance is associated with the severity of COVID-19. However, the long-term effects of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection on LDG levels and phenotypic alteration remain unexplored.

Methods

Using participants naïve to SARS-CoV-2 (NP), infected with SARS-CoV-2 with no residual symptoms (NRS), and infected with SARS-CoV-2 with chronic pulmonary symptoms (PPASC), we compared LDG levels and their phenotype by measuring the expression of markers for activation, maturation, and neutrophil extracellular trap (NET) formation using flow cytometry.

Results

The number of LDGs was elevated in PPASC compared to NP. Individuals infected with SARS-CoV-2 (NRS and PPASC) demonstrated increased CD10+ and CD16hi subset counts of LDGs compared to NP group. Further characterization of LDGs demonstrated that LDGs from COVID-19 convalescents (PPASC and NRS) displayed increased markers of NET forming ability and aggregation with platelets compared to LDGs from NP, but no differences were observed between PPASC and NRS.

Conclusions

Our data from a small cohort study demonstrates that mature neutrophils with a heightened activation phenotype remain in circulation long after initial SARS-CoV-2 infection. Persistent elevation of markers for neutrophil activation and NET formation on LDGs, as well as an enhanced proclivity for platelet-neutrophil aggregation (PNA) formation in COVID-19 convalescent individuals may be associated with PPASC prognosis and development.