Impact of human airway epithelial cellular composition on SARS-CoV-2 infection biology

Infection biology and pathogenesis of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of the coronavirus disease 2019 (COVID-19), are incompletely understood. Here, we assessed the impact of airway epithelial cellular composition on infection in air-liquid interface (ALI) cultures of differentiated primary human tracheal (PTEC) and bronchial epithelial cells (PBEC). We first compared SARS-CoV-2 infection kinetics, related antiviral and inflammatory responses, and viral entry factors in PTEC and PBEC. Next, the contribution of differentiation time was investigated by differentiating ALI-PTEC/PBEC for 3-5 weeks and comparing dynamics of viral replication/spread, cellular composition and epithelial responses. We observed a gradual increase in viral load with prolonged culture duration. Ciliated and goblet cells were predominantly infected in both PTEC and PBEC. Immunofluorescence analysis and RT-qPCR showed that compared to other cell types mainly ciliated and goblet cell numbers were affected by increased culture duration. An increased proportion of these two target cell types was associated with increased viral load. Furthermore, modulation of cellular composition using IL-13 and the Notch signaling inhibitor DAPT, underlined the importance of both ciliated and goblet cells for infection. DAPT treatment resulted in a lower viral load and a relative increase in ciliated cells at the expense of goblet cells, compared to IL-13 treated cultures in which both cell types were present and viral load was higher. In conclusion, our results identify cellular composition as a contributing factor to airway epithelial susceptibility to SARS-CoV-2. IMPORTANCEIn this study, we determined an effect of culture duration and airway cellular composition of ALI-PBEC and ALI-PTEC cultures on SARS-CoV-2 infection. We found that SARS-CoV-2 infection was increased with prolonged cell culture time and the total percentage and proportion of ciliated and goblet cells played an important role in infection level, suggesting that airway epithelial differentiation/maturation levels may in part determine susceptibility of SARS-CoV-2 infection. The development of effective therapies either targeting virus replication or pathogenesis against SARS-CoV-2 requires robust cell culture-based infection models to test small molecules and biologicals. Therefore, it is important to identify factors that are essential for reliably modeling SARS-CoV-2-airway epithelial cell interactions. This study sheds light on virus-airway epithelial cell interactions and adds to the complexity of SARS-CoV-2 cell tropism in the airways. In addition, the effect of IL-13 on viral infection hints at a causal connection between SARS-CoV-2 infection and (allergic) asthma.

Differential interferon-α subtype immune signatures suppress SARS-CoV-2 infection

Type I interferons (IFN-I) exert pleiotropic biological effects during viral infections, balancing virus control versus immune-mediated pathologies and have been successfully employed for the treatment of viral diseases. Humans express twelve IFN-alpha () subtypes, which activate downstream signalling cascades and result in distinct patterns of immune responses and differential antiviral responses. Inborn errors in type I IFN immunity and the presence of anti-IFN autoantibodies account for very severe courses of COVID-19, therefore, early administration of type I IFNs may be protective against life-threatening disease. Here we comprehensively analysed the antiviral activity of all IFN subtypes against SARS-CoV-2 to identify the underlying immune signatures and explore their therapeutic potential. Prophylaxis of primary human airway epithelial cells (hAEC) with different IFN subtypes during SARS-CoV-2 infection uncovered distinct functional classes with high, intermediate and low antiviral IFNs. In particular IFN5 showed superior antiviral activity against SARS-CoV-2 infection. Dose-dependency studies further displayed additive effects upon co-administered with the broad antiviral drug remdesivir in cell culture. Transcriptomics of IFN-treated hAEC revealed different transcriptional signatures, uncovering distinct, intersecting and prototypical genes of individual IFN subtypes. Global proteomic analyses systematically assessed the abundance of specific antiviral key effector molecules which are involved in type I IFN signalling pathways, negative regulation of viral processes and immune effector processes for the potent antiviral IFN5. Taken together, our data provide a systemic, multi-modular definition of antiviral host responses mediated by defined type I IFNs. This knowledge shall support the development of novel therapeutic approaches against SARS-CoV-2.

Seasonality of non-SARS, non-MERS Corona viruses and the impact of meteorological factors

BackgroundSeasonality is a characteristic of some respiratory viruses. The aim of our study was to evaluate the seasonality and the potential effects of different meteorological factors on the detection rate of the non-SARS Corona Virus detection by PCR. MethodsWe performed a retrospective analysis of 12763 respiratory tract sample results (288 positive and 12475 negative) for non-SARS, non-MERS Corona viruses (NL63, 229E, OC43, HKU1). The effect of seven single weather factors on the Corona virus detection rate was fitted in a logistic regression model with and without adjusting for other weather factors. ResultsCorona virus infections followed a seasonal pattern peaking from December to March and plunging from July to September. The seasonal effect was less pronounced in immunosuppressed patients compared to immunocompetent. Different automatic variable selection processes agreed to select the predictors temperature, relative humidity, cloud cover and precipitation as remaining predictors in the multivariable logistic regression model including all weather factors, with low ambient temperature, low relative humidity, high cloud cover and high precipitation being linked to increased Corona virus detection rates. ConclusionsCorona virus infections followed a seasonal pattern, which was more pronounced in immunocompetent patients compared to immunosuppressed. Several meteorological factors were associated with the Corona virus detection rate. However, when mutually adjusting for all weather factors, only temperature, relative humidity, precipitation and cloud cover contributed independently to predicting the Corona virus detection rate.

Immunomodulatory Effects of Ambroxol on Airway Hyperresponsiveness and Inflammation

Ambroxol is used in COPD and asthma to increase mucociliary clearance and regulate surfactant levels, perhaps through anti-oxidant and anti-inflammatory activities. To determine the role and effect of ambroxol in an experimental model of asthma, BALB/c mice were sensitized to ovalbumin (OVA) followed by 3 days of challenge. Airway hyperresponsiveness (AHR), lung cell composition and histology, and cytokine and protein carbonyl levels in bronchoalveolar lavage (BAL) fluid were determined. Ambroxol was administered either before the first OVA challenge or was begun after the last allergen challenge. Cytokine production levels from lung mononuclear cells (Lung MNCs) or alveolar macrophages (AM) were also determined. Administration of ambroxol prior to challenge suppressed AHR, airway eosinophilia, goblet cell metaplasia, and reduced inflammation in subepithelial regions. When given after challenge, AHR was suppressed but without effects on eosinophil numbers. Levels of IL-5 and IL-13 in BAL fluid were decreased when the drug was given prior to challenge; when given after challenge, increased levels of IL-10 and IL-12 were detected. Decreased levels of protein carbonyls were detected in BAL fluid following ambroxol treatment after challenge. In vitro, ambroxol increased levels of IL-10, IFN-γ, and IL-12 from Lung MNCs and AM, whereas IL-4, IL-5, and IL-13 production was not altered. Taken together, ambroxol was effective in preventing AHR and airway inflammation through upregulation of Th1 cytokines and protection from oxidative stress in the airways.

Mast Cells in Allergic Asthma and Beyond

Mast cells have been regarded for a long time as effector cells in IgE mediated type I reactions and in host defence against parasites. However, they are resident in all environmental exposed tissues and express a wide variety of receptors, suggesting that these cells can also function as sentinels in innate immune responses. Indeed, studies have demonstrated an important role of mast cells during the induction of life-saving antibacterial responses. Furthermore, recent findings have shown that mast cells promote and modulate the development of adaptive immune responses, making them an important hinge of innate and acquired immunity. In addition, mast cells and several mast cell-produced mediators have been shown to be important during the development of allergic airway diseases. In the present review, we will summarize findings on the role of mast cells during the development of adaptive immune responses and highlight their function, especially during the development of allergic asthma.