Infection of primary nasal epithelial cells differentiates among lethal and seasonal human coronaviruses.

The nasal epithelium is the initial entry portal and primary barrier to infection by all human coronaviruses (HCoVs). We utilize primary human nasal epithelial cells grown at air-liquid interface, which recapitulate the heterogeneous cellular population as well as mucociliary clearance functions of the in vivo nasal epithelium, to compare lethal [Severe acute respiratory syndrome (SARS)-CoV-2 and Middle East respiratory syndrome-CoV (MERS-CoV)] and seasonal (HCoV-NL63 and HCoV-229E) HCoVs. All four HCoVs replicate productively in nasal cultures, though replication is differentially modulated by temperature. Infections conducted at 33 °C vs. 37 °C (reflective of temperatures in the upper and lower airway, respectively) revealed that replication of both seasonal HCoVs (HCoV-NL63 and -229E) is significantly attenuated at 37 °C. In contrast, SARS-CoV-2 and MERS-CoV replicate at both temperatures, though SARS-CoV-2 replication is enhanced at 33 °C late in infection. These HCoVs also diverge significantly in terms of cytotoxicity induced following infection, as the seasonal HCoVs as well as SARS-CoV-2 cause cellular cytotoxicity as well as epithelial barrier disruption, while MERS-CoV does not. Treatment of nasal cultures with type 2 cytokine IL-13 to mimic asthmatic airways differentially impacts HCoV receptor availability as well as replication. MERS-CoV receptor DPP4 expression increases with IL-13 treatment, whereas ACE2, the receptor used by SARS-CoV-2 and HCoV-NL63, is down-regulated. IL-13 treatment enhances MERS-CoV and HCoV-229E replication but reduces that of SARS-CoV-2 and HCoV-NL63, reflecting the impact of IL-13 on HCoV receptor availability. This study highlights diversity among HCoVs during infection of the nasal epithelium, which is likely to influence downstream infection outcomes such as disease severity and transmissibility.

SARS-CoV-2 infection of airway cells causes intense viral and cell shedding, two spreading mechanisms affected by IL-13.

Muco-obstructive lung diseases are typically associated with high risks of COVID-19 severity; however, allergic asthma showed reduced susceptibility. To investigate viral spread, primary human airway epithelial (HAE) cell cultures were infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and host­virus interactions were examined via electron microscopy, immunohistochemistry, RNA in situ hybridization, and gene expression analyses. In HAE cell cultures, angiotensin-converting enzyme 2 (ACE2) expression governed cell tropism and viral load and was up-regulated by infection. Electron microscopy identified intense viral egress from infected ciliated cells and severe cytopathogenesis, culminating in the shedding of ciliated cells packed with virions, providing a large viral reservoir for spread and transmission. Intracellular stores of MUC5AC, a major airway mucin involved in asthma, were rapidly depleted, likely to trap viruses. To mimic asthmatic airways, HAE cells were treated with interleukin-13 (IL-13), which reduced viral titers, viral messenger RNA, and cell shedding, and significantly diminished the number of infected cells. Although mucus hyperproduction played a shielding role, IL-13­treated cells maintained a degree of protection despite the removal of mucus. Using Gene Expression Omnibus databases, bulk RNA-sequencing analyses revealed that IL-13 up-regulated genes controlling glycoprotein synthesis, ion transport, and antiviral processes (albeit not the typical interferon-induced genes) and down-regulated genes involved in cilial function and ribosomal processing. More precisely, we showed that IL-13 reduced ACE2 expression, intracellular viral load, and cell-to-cell transmission while increasing the cilial keratan sulfate coating. In conclusion, intense viral and cell shedding caused by SARS-CoV-2 infection was attenuated by IL-13, which affected viral entry, replication, and spread.

SARS-CoV-2 Induces Cytokine Responses in Human Basophils.

Basophils play a key role in the orientation of immune responses. Though the interaction of SARS-CoV-2 with various immune cells has been relatively well studied, the response of basophils to this pandemic virus is not characterized yet. In this study, we report that SARS-CoV-2 induces cytokine responses and in particular IL-13, in both resting and IL-3 primed basophils. The response was prominent under IL-3 primed condition. However, either SARS-CoV-2 or SARS-CoV-2-infected epithelial cells did not alter the expression of surface markers associated with the activation of basophils, such as CD69, CD13 and/or degranulation marker CD107a. We also validate that human basophils are not permissive to SARS-CoV-2 replication. Though increased expression of immune checkpoint molecule PD-L1 has been reported on the basophils from COVID-19 patients, we observed that SARS-CoV-2 does not induce PD-L1 on the basophils. Our data suggest that basophil cytokine responses to SARS-CoV-2 might help in reducing the inflammation and also to promote antibody responses to the virus.

Recent Advances in the Inhibition of the IL-4 Cytokine Pathway for the Treatment of Allergen-Induced Asthma.

The IL-4 and IL-13 cytokine pathways play integral roles in stimulating IgE inflammation, with the IL-4 cytokine being a major cytokine in the etiology of thunderstorm asthma, atopic dermatitis, and allergic rhinitis. The increasing prevalence of thunderstorm asthma in the younger population and the lessening efficacy of corticosteroids and other anti-inflammatories has created a need for more effective pharmaceuticals. This review summarizes the IL-4 and IL-13 pathways while highlighting and discussing the current pathway inhibitors aimed at treating thunderstorm asthma and atopic dermatitis, as well as the potential efficacy of peptide therapeutics in this field.

IL-4/IL-13 remodeling pathway of COVID-19 lung injury.

The COVID-19 fatality rate is high when compared to the H1N1pdm09 (pandemic Influenza A virus H1N1 subtype) rate, and although both cause an aggravated inflammatory response, the differences in the mechanisms of both pandemic pneumonias need clarification. Thus, our goal was to analyze tissue expression of interleukins 4, 13, (IL-4, IL-13), transforming growth factor-beta (TGF-ß), and the number of M2 macrophages (Sphingosine-1) in patients who died by COVID-19, comparing with cases of severe pneumopathy caused by H1N1pdm09, and a control group without lung injury. Six lung biopsy samples of patients who died of SARS-CoV-2 (COVID-19 group) were used and compared with ten lung samples of adults who died from a severe infection of H1N1pdm09 (H1N1 group) and eleven samples of patients who died from different causes without lung injury (CONTROL group). The expression of IL-4, IL-13, TGF-ß, and M2 macrophages score (Sphingosine-1) were identified through immunohistochemistry (IHC). Significantly higher IL-4 tissue expression and Sphingosine-1 in M2 macrophages were observed in the COVID-19 group compared to both the H1N1 and the CONTROL groups. A different mechanism of diffuse alveolar damage (DAD) in SARS-CoV-2 compared to H1N1pdm09 infections were observed. IL-4 expression and lung remodeling are phenomena observed in both SARS-CoV-2 and H1N1pdm09. However, SARS-CoV-2 seems to promote lung damage through different mechanisms, such as the scarce participation Th1/Th17 response and the higher participation of the Th2. Understanding and managing the aggravated and ineffective immune response elicited by SARS-CoV-2 merits further clarification to improve treatments propose.

Type 2 and interferon inflammation regulate SARS-CoV-2 entry factor expression in the airway epithelium.

Coronavirus disease 2019 (COVID-19) is caused by SARS-CoV-2, an emerging virus that utilizes host proteins ACE2 and TMPRSS2 as entry factors. Understanding the factors affecting the pattern and levels of expression of these genes is important for deeper understanding of SARS-CoV-2 tropism and pathogenesis. Here we explore the role of genetics and co-expression networks in regulating these genes in the airway, through the analysis of nasal airway transcriptome data from 695 children. We identify expression quantitative trait loci for both ACE2 and TMPRSS2, that vary in frequency across world populations. We find TMPRSS2 is part of a mucus secretory network, highly upregulated by type 2 (T2) inflammation through the action of interleukin-13, and that the interferon response to respiratory viruses highly upregulates ACE2 expression. IL-13 and virus infection mediated effects on ACE2 expression were also observed at the protein level in the airway epithelium. Finally, we define airway responses to common coronavirus infections in children, finding that these infections generate host responses similar to other viral species, including upregulation of IL6 and ACE2. Our results reveal possible mechanisms influencing SARS-CoV-2 infectivity and COVID-19 clinical outcomes.