The emergence of SARS-CoV-2 variants of concern with progressively increased transmissibility between humans is a threat to global public health. The Omicron variant of SARS-CoV-2 also evades ...immunity from natural infection or vaccines
, but it is unclear whether its exceptional transmissibility is due to immune evasion or intrinsic virological properties. Here we compared the replication competence and cellular tropism of the wild-type virus and the D614G, Alpha (B.1.1.7), Beta (B.1.351), Delta (B.1.617.2) and Omicron (B.1.1.529) variants in ex vivo explant cultures of human bronchi and lungs. We also evaluated the dependence on TMPRSS2 and cathepsins for infection. We show that Omicron replicates faster than all other SARS-CoV-2 variants studied in the bronchi but less efficiently in the lung parenchyma. All variants of concern have similar cellular tropism compared to the wild type. Omicron is more dependent on cathepsins than the other variants of concern tested, suggesting that the Omicron variant enters cells through a different route compared with the other variants. The lower replication competence of Omicron in the human lungs may explain the reduced severity of Omicron that is now being reported in epidemiological studies, although determinants of severity are multifactorial. These findings provide important biological correlates to previous epidemiological observations.
Abstract
Background
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is an emerging coronavirus that has resulted in more than 2 000 000 laboratory-confirmed cases including over 145 000 ...deaths. Although SARS-CoV-2 and SARS-CoV share a number of common clinical manifestations, SARS-CoV-2 appears to be highly efficient in person-to-person transmission and frequently causes asymptomatic or presymptomatic infections. However, the underlying mechanisms that confer these viral characteristics of high transmissibility and asymptomatic infection remain incompletely understood.
Methods
We comprehensively investigated the replication, cell tropism, and immune activation profile of SARS-CoV-2 infection in human lung tissues with SARS-CoV included as a comparison.
Results
SARS-CoV-2 infected and replicated in human lung tissues more efficiently than SARS-CoV. Within the 48-hour interval, SARS-CoV-2 generated 3.20-fold more infectious virus particles than did SARS-CoV from the infected lung tissues (P < .024). SARS-CoV-2 and SARS-CoV were similar in cell tropism, with both targeting types I and II pneumocytes and alveolar macrophages. Importantly, despite the more efficient virus replication, SARS-CoV-2 did not significantly induce types I, II, or III interferons in the infected human lung tissues. In addition, while SARS-CoV infection upregulated the expression of 11 out of 13 (84.62%) representative proinflammatory cytokines/chemokines, SARS-CoV-2 infection only upregulated 5 of these 13 (38.46%) key inflammatory mediators despite replicating more efficiently.
Conclusions
Our study provides the first quantitative data on the comparative replication capacity and immune activation profile of SARS-CoV-2 and SARS-CoV infection in human lung tissues. Our results provide important insights into the pathogenesis, high transmissibility, and asymptomatic infection of SARS-CoV-2.
The comparative viral kinetics, cell tropism, and innate immune response profiles of SARS-CoV-2 and SARS-CoV in human lungs were characterized in ex vivo organ cultures. SARS-CoV-2 exhibited more efficient replication but induced significantly less host interferon and proinflammatory response than SARS-CoV.
Understanding the factors that contribute to efficient SARS-CoV-2 infection of human cells may provide insights on SARS-CoV-2 transmissibility and pathogenesis, and reveal targets of intervention. ...Here, we analyze host and viral determinants essential for efficient SARS-CoV-2 infection in both human lung epithelial cells and ex vivo human lung tissues. We identify heparan sulfate as an important attachment factor for SARS-CoV-2 infection. Next, we show that sialic acids present on ACE2 prevent efficient spike/ACE2-interaction. While SARS-CoV infection is substantially limited by the sialic acid-mediated restriction in both human lung epithelial cells and ex vivo human lung tissues, infection by SARS-CoV-2 is limited to a lesser extent. We further demonstrate that the furin-like cleavage site in SARS-CoV-2 spike is required for efficient virus replication in human lung but not intestinal tissues. These findings provide insights on the efficient SARS-CoV-2 infection of human lungs.
Interferons (IFNs) are critical for immune defense against pathogens. While type‐I and ‐III IFNs have been reported to inhibit SARS‐CoV‐2 replication, the antiviral effect and mechanism of type‐II ...IFN against SARS‐CoV‐2 remain largely unknown. Here, we evaluate the antiviral activity of type‐II IFN (IFNγ) using human lung epithelial cells (Calu3) and ex vivo human lung tissues. In this study, we found that IFNγ suppresses SARS‐CoV‐2 replication in both Calu3 cells and ex vivo human lung tissues. Moreover, IFNγ treatment does not significantly modulate the expression of SARS‐CoV‐2 entry‐related factors and induces a similar level of pro‐inflammatory response in human lung tissues when compared with IFNβ treatment. Mechanistically, we show that overexpression of indoleamine 2,3‐dioxygenase 1 (IDO1), which is most profoundly induced by IFNγ, substantially restricts the replication of ancestral SARS‐CoV‐2 and the Alpha and Delta variants. Meanwhile, loss‐of‐function study reveals that IDO1 knockdown restores SARS‐CoV‐2 replication restricted by IFNγ in Calu3 cells. We further found that the treatment of l‐tryptophan, a substrate of IDO1, partially rescues the IFNγ‐mediated inhibitory effect on SARS‐CoV‐2 replication in both Calu3 cells and ex vivo human lung tissues. Collectively, these results suggest that type‐II IFN potently inhibits SARS‐CoV‐2 replication through IDO1‐mediated antiviral response.
Highly pathogenic coronaviruses, including severe acute respiratory syndrome coronavirus 2 (refs.
) (SARS-CoV-2), Middle East respiratory syndrome coronavirus
(MERS-CoV) and SARS-CoV-1 (ref.
), ...vary in their transmissibility and pathogenicity. However, infection by all three viruses results in substantial apoptosis in cell culture
and in patient tissues
, suggesting a potential link between apoptosis and pathogenesis of coronaviruses. Here we show that caspase-6, a cysteine-aspartic protease of the apoptosis cascade, serves as an important host factor for efficient coronavirus replication. We demonstrate that caspase-6 cleaves coronavirus nucleocapsid proteins, generating fragments that serve as interferon antagonists, thus facilitating virus replication. Inhibition of caspase-6 substantially attenuates lung pathology and body weight loss in golden Syrian hamsters infected with SARS-CoV-2 and improves the survival of mice expressing human DPP4 that are infected with mouse-adapted MERS-CoV. Our study reveals how coronaviruses exploit a component of the host apoptosis cascade to facilitate virus replication.
The Model for End-stage Liver Disease excluding international normalized ratio (MELD-XI) score and the modified MELD score with albumin replacing international normalized ratio (MELD-Albumin) score, ...which reflect both liver and renal function, have been reported as predictors of adverse events in liver and heart disease. Nonetheless, their prognostic value in patients undergoing tricuspid annuloplasty has not been addressed.
A total of 394 patients who underwent tricuspid annuloplasty were evaluated. Baseline clinical, laboratory, and echocardiographic parameters were recorded. Adverse outcome was defined as the occurrence of heart failure requiring admission or all-cause mortality. Patients who underwent tricuspid annuloplasty had a high prevalence of preoperative hepatorenal dysfunction that was more common in patients with severe tricuspid regurgitation than those with mild to moderate tricuspid regurgitation. The MELD-XI and MELD-Albumin scores were excellent predictors of 1-year adverse outcome (area under the curve: 0.69 and 0.75, respectively). Kaplan-Meier survival curve demonstrated that a high score on MELD-XI (≥12.0) and MELD-Albumin (≥10.7) was associated with an increased risk of adverse events. During a median follow-up of 40 months, both MELD-XI and MELD-Albumin scores were significantly associated with adverse outcome, even after adjusting for potential confounding factors. Significant improvement of hepatorenal function at 1 year postoperation was noted only in patients who had no adverse events, not in those who experienced an adverse outcome.
Both MELD-XI score and MELD-Albumin score can provide useful information to predict adverse outcome in patients undergoing tricuspid annuloplasty. The present study supports monitoring of modified MELD score to improve preoperative risk stratification of these patients.
Human infection with avian influenza A(H3N8) virus is uncommon but can lead to acute respiratory distress syndrome. In explant cultures of the human bronchus and lung, novel H3N8 virus showed limited ...replication efficiency in bronchial and lung tissue but had a higher replication than avian H3N8 virus in lung tissue.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, ODKLJ, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The Omicron BA.2 sublineage has replaced BA.1 worldwide and has comparable levels of immune evasion to BA.1. These observations suggest that the increased transmissibility of BA.2 cannot be explained ...by the antibody evasion.
Here, we characterized the replication competence and respiratory tissue tropism of three Omicron variants (BA.1, BA.1.1, BA.2), and compared these with the wild-type virus and Delta variant, in human nasal, bronchial and lung tissues cultured ex vivo.
BA.2 replicated more efficiently in nasal and bronchial tissues at 33°C than wild-type, Delta and BA.1. Both BA.2 and BA.1 had higher replication competence than wild-type and Delta viruses in bronchial tissues at 37°C. BA.1, BA.1.1 and BA.2 replicated at a lower level in lung parenchymal tissues compared to wild-type and Delta viruses.
Higher replication competence of Omicron BA.2 in the human upper airway at 33°C than BA.1 may be one of the reasons to explain the current advantage of BA.2 over BA.1. A lower replication level of the tested Omicron variants in human lung tissues is in line with the clinical manifestations of decreased disease severity of patients infected with the Omicron strains compared with other ancestral strains.
This work was supported by US National Institute of Allergy and Infectious Diseases and the Theme-Based Research Scheme under University Grants Committee of Hong Kong Special Administrative Region, China.
Abstract
The airways and alveoli of the human respiratory tract are lined by two distinct types of epithelium, which are the primary targets of respiratory viruses. We previously established ...long-term expanding human lung epithelial organoids from lung tissues and developed a ‘proximal’ differentiation protocol to generate mucociliary airway organoids. However, a respiratory organoid system with bipotential of the airway and alveolar differentiation remains elusive. Here we defined a ‘distal’ differentiation approach to generate alveolar organoids from the same source for the derivation of airway organoids. The alveolar organoids consisting of type I and type II alveolar epithelial cells (AT1 and AT2, respectively) functionally simulate the alveolar epithelium. AT2 cells maintained in lung organoids serve as progenitor cells from which alveolar organoids derive. Moreover, alveolar organoids sustain a productive SARS-CoV-2 infection, albeit a lower replicative fitness was observed compared to that in airway organoids. We further optimized 2-dimensional (2D) airway organoids. Upon differentiation under a slightly acidic pH, the 2D airway organoids exhibit enhanced viral replication, representing an optimal in vitro correlate of respiratory epithelium for modeling the high infectivity of SARS-CoV-2. Notably, the higher infectivity and replicative fitness of the Omicron variant than an ancestral strain were accurately recapitulated in these optimized airway organoids. In conclusion, we have established a bipotential organoid culture system able to reproducibly expand the entire human respiratory epithelium in vitro for modeling respiratory diseases, including COVID-19.
PDF
