Atypical N-glycosylation of SARS-CoV-2 impairs the efficient binding of Spike-RBM to the human-host receptor hACE2 (preprint)

SARS-CoV-2 internalization by human host cells relies on the molecular binding of its spike glycoprotein (SGP) to the angiotensin-converting-enzyme-2 (hACE2) receptor. It remains unknown whether atypical N-glycosylation of SGP modulates SARS-CoV-2 tropism for infections. Here, we address this question through an extensive bioinformatics analysis of publicly available structural and genetic data. We identified two atypical sequons (sequences of N-glycosylation: NGV 481-483 and NGV 501-503), strategically located on the receptor-binding motif (RBM) of SGP and facing the hACE2 receptor. Interestingly, the cryo-electron microscopy structure of trimeric SGP in complex with potent-neutralizing antibodies from convalescent patients revealed covalently-linked N-glycans in NGV 481-483 atypical sequons. Furthermore, NGV 501-503 atypical sequon involves the asparagine-501 residue, whose highly-transmissible mutation N501Y is present in circulating variants of major concerns and affects the SGP-hACE2 binding-interface through the well-known hotspot-353. These findings suggest that atypical SGP post-translational modifications modulate the SGP-hACE2 binding-affinity affecting consequently SARS-CoV-2 transmission and pathogenesis.

Blunted Fas signaling favors RIPK1-driven neutrophil necroptosis in critically ill COVID-19 patients (preprint)

Critically ill COVID-19 patients are characterized by a severely dysregulated cytokine profile and elevated neutrophil counts, which are thought to contribute to disease severity. However, to date it remains unclear how neutrophils contribute to pathophysiology during COVID-19. Here, we assessed the impact of the dysregulated cytokine profile on the tightly regulated cell death program of neutrophils. We show that in a subpopulation of neutrophils, canonical apoptosis was skewed towards rapidly occurring necroptosis. This phenotype was characterized by abrogated caspase-8 activity and increased RIPK1 levels, favoring execution of necroptosis via the RIPK1-RIPK3-MLKL axis, as further confirmed in COVID-19 biopsies. Moreover, reduction of sFas-L levels in COVID-19 patients and hence decreased signaling to Fas directly increased RIPK1 levels and correlated with disease severity. Our results suggest an important role for Fas signaling in the regulation of cell death program ambiguity via the ripoptosome in neutrophils during COVID-19 and a potential therapeutic target to curb inflammation and thus influence disease severity and outcome.

Neutrophil and monocyte dysfunctional effector response towards bacterial challenge in critically-ill COVID-19 patients (preprint)

COVID-19 displays diverse disease severities and symptoms. Elevated inflammation mediated by hypercytokinemia induces a detrimental dysregulation of immune cells. However, there is limited understanding of how SARS-CoV-2 pathogenesis impedes innate immune signaling and function against secondary bacterial infections. We assessed the influence of COVID-19 hypercytokinemia on the functional responses of neutrophils and monocytes upon bacterial challenges from acute and corresponding recovery COVID-19 ICU patients. We show that severe hypercytokinemia in COVID-19 patients correlated with bacterial superinfections. Neutrophils and monocytes from acute COVID-19 patients showed severely impaired microbicidal capacity, reflected by abrogated ROS and MPO production as well as reduced NETs upon bacterial challenges. We observed a distinct pattern of cell surface receptor expression on both neutrophils and monocytes leading to a suppressive autocrine and paracrine signaling during bacterial challenges. Our data provide insights into the innate immune status of COVID-19 patients mediated by their hypercytokinemia and its transient effect on immune dysregulation upon subsequent bacterial infections

Bacterial pulmonary superinfections are associated with unfavourable outcomes in critically ill COVID-19 patients (preprint)

Objectives While superinfections are associated with unfavourable disease course, their impact on clinical outcomes in critically ill COVID-19 patients remains largely unknown. We aimed to investigate the burden of superinfections in COVID-19 patients. Methods In this prospective single centre cohort study in an intensive care setting patients aged [≥] 18 years with COVID-19 acute respiratory distress syndrome were assessed for concomitant microbial infections by longitudinal analysis of tracheobronchial secretions, bronchoalveolar lavages and blood. Our primary outcome was ventilator-free survival on day 28 in patients with and without clinically relevant superinfection. Further outcomes included the association of superinfection with ICU length of stay, incidence of bacteremia, viral reactivations, and fungal colonization. Results In 45 critically ill COVID-19 patients, we identified 19 patients with superinfections (42.2%) by longitudinal analysis of 433 TBS, 35 BAL and 455 blood samples, respectively. On average, superinfections were detected on day 10 after ICU admission. The most frequently isolated clinically relevant bacteria were Enterobacteriaceae, Streptococcus pneumoniae, and Pseudomonas aeruginosa. Ventilator-free survival was substantially lower in patients with superinfection (subhazard ratio 0.37, 95%-CI 0.15-0.90, p=0.028). Patients with pulmonary superinfections more often had bacteraemia, virus reactivations, yeast colonization, and needed ICU treatment for a significantly longer time. Conclusions The detection of superinfections was frequent and associated with reduced ventilator-free survival. Despite empirical antibiotic therapy, superinfections lead to an extended ICU stay in COVID 19 patients. Longitudinal microbiological sampling in COVID-19 patients could allow targeted antimicrobial therapy, and therefore minimize the use of broad-spectrum and reserve antibiotics.

Severe COVID-19 is associated with elevated serum IgA and antiphospholipid IgA-antibodies (preprint)

BackgroundWhile the pathogenesis of coronavirus disease 2019 (COVID-19) is becoming increasingly clear, there is little data on IgA response, the first line of bronchial immune defense. ObjectiveTo determine, whether COVID-19 is associated with a vigorous total IgA response and whether IgA autoantibodies are associated with complications of severe illness. Since thrombotic events are frequent in severe COVID-19 and resemble hypercoagulation of antiphospholipid syndrome (APS), our approach focused on antiphospholipid antibodies (aPL). Materials and methodsIn this retrospective cohort study we compared clinical data and aPL from 64 patients with COVID-19 from three independent centers (two in Switzerland, one in Liechtenstein). Samples were collected from April 9, 2020 to May 1, 2020. Total IgA and aPL were measured with FDA-approved commercially available clinical diagnostic kits. ResultsClinical records of the 64 patients with COVID-19 were reviewed and divided into a cohort with mild illness (mCOVID, n=26 [41%]), a discovery cohort with severe illness (sdCOVD, n=14 [22%]) and a confirmation cohort with severe illness (scCOVID, n=24 [38%]). Severe illness was significantly associated with increased total IgA (sdCOVID, P=0.01; scCOVID, P<0.001). Total IgG levels were similar in both cohorts. Among aPL, both cohorts with severe illness significantly correlated with elevated anti-Cardiolipin IgA (sdCOVID and scCOVID, P<0.001), anti-Cardiolipin IgM (sdCOVID, P=0.003; scCOVID, P<0.001), and anti-Beta2 Glycoprotein-1 IgA (sdCOVID and scCOVID, P<0.001). Systemic lupus erythematosus was excluded from all patients as a potential confounder of APS. ConclusionsHigher total IgA and IgA-aPL were consistently associated with severe illness. These novel data strongly suggest that a vigorous antiviral IgA-response triggered in the bronchial mucosa induces systemic autoimmunity.