The Respiratory Epithelium and Viral Infection
There is no time like the present, while the world is fighting the virus that causes COVID-19 (SARS-CoV-2), to appreciate the deadly effects of respiratory viruses. Respiratory viruses like influenza and coronaviruses infect the epithelium of the airway, which lines the inner surface of the trachea, bronchi, bronchioles, and lung alveoli. The respiratory epithelium is designed to help defend against pathogenic infection through secretion of a mucus layer, as well as through the action of cilia that direct particles away from the lungs, back toward the larynx, where air first enters the respiratory system.
Check out the Lifeline® catalog for our human bronchial/tracheal epithelial cells, as well as the rest of our lung and airway cells, which includes:
- Small airway cells
- Diseased small airway epithelial cells – asthma and COPD
- Bronchial/tracheal epithelial cells
- Diseased bronchial/tracheal epithelial cells – cystic fibrosis
- Bronchial/tracheal smooth muscle cells
- Lobar bronchial epithelial cells
- Lung microvascular endothelial cells
- Lung fibroblasts
- Lung smooth muscle cells
- Laryngeal epithelial cells
Lifeline Human Bronchial/Tracheal Epithelial Cells in Coronavirus, Influenza Virus, and Respiratory Syncytial Virus Research
Middle East respiratory syndrome, or MERS, is caused by a coronavirus (CoV), specifically by MERS-CoV. To contain outbreaks of MERS, rapid and efficient testing and diagnosis is crucial; however, the test currently recommended by the World Health Organization can be time consuming and requires laboratory equipment. The diagnostic test for MERS looks for two parts of the viral genome, which are detected using real-time reverse transcription polymerase chain reaction (RT-PCR) assays. In a 2019 study, Shirato and colleagues (opens in new window) describe the development of a new RT-PCR system using the PicoGene PCR1100 device, an ultra-rapid mobile PCR device.
Using a Corman assay, which detects the upE and open reading frame (ORF) 1a regions of the MERS-CoV viral genome in two separate, sequential tests, the authors tested the sensitivity of their ultra-rapid real-time RT-PCR method and found that five copies of viral RNA were sufficient for detection with no cross-reaction with other respiratory viral genomes. The authors used Lifeline human bronchial/tracheal epithelial cells (HBTECs) cultured in an air-liquid interface to propagate other clinical coronavirus specimens (HCoV-OC43, HCoV-HKU1, and HCoV-NL63) as negative controls to demonstrate that their results were specific to MERS-CoV.
The authors also performed spike tests, in which they tested the specificity of their assay using MERS-CoV viral isolates mixed with clinical specimens, including nasopharyngeal swab, nasal swab, sputum, and bronchoalveolar lavage samples to mimic the samples that would be taken from patients. Their results showed that the ultra-rapid real-time mobile RT-PCR assay was sensitive enough to detect viral RNA in respiratory tract samples.
Together, the results of this study illustrate the utility of a faster diagnostic test for MERS-CoV without loss of specificity.
Two viruses that have a deadly toll every year are the influenza virus and respiratory syncytial virus (RSV). Although a vaccine exists to protect against influenza, it is not 100% effective and the elderly population, in particular, has a high risk of infection; no vaccine exists for RSV. Therefore, antiviral agents for the treatment of influenza and RSV are urgently needed, particularly those with a wide range of influenza-like indications.
To evaluate potential such broad-spectrum antiviral candidate compounds, Yoon and colleagues developed a high-throughput assay to identify molecules that inhibit both influenza and RSV. When the group tested a library of 102 ribonucleoside analog compounds, they found only one candidate (N4-hydroxycytidine; NHC) was active against the panel of influenza viruses and RSVs tested, including clinical RSV isolates; human, avian, and swine influenza A viruses; and influenza B viruses. Using Lifeline HBTECs to propagate influenza A virus and RSV samples, the authors showed that NHC had antiviral activity in cultured primary human respiratory epithelial cells.
Using polymerase activity assays and sequencing, the authors found that NHC acts by incorporating into the viral genome and causing mutations. Following pharmacokinetic and pharmacodynamic analyses in HBTECs and mice, the group found that NHC-TP (the active form of the compound) had a half-life longer than four hours and an oral bioavailability of 36-56%.
Next, the authors tested the efficacy of NHC-TP in vivo using mice infected with RSV-A2-L19F and the H1N1 influenza viruses. They began by testing NHC-TP at 100 mg/kg and 400 mg/kg twice per day, starting two hours before infection and up to five (RSV) or six (influenza) days post-infection. Compared with vehicle-treated mice, mice treated with NHC had significantly lower RSV or influenza viral load and reduced pathogenesis of infection, including lower mucin production (RSV) or ameliorated hyperthermia symptoms (influenza).
The authors next tested the efficacy of 400 mg/kg NHC against the highly pathogenic H5N1 influenza virus and found that six days post-infection, mice treated with NHC had significantly lower viral titers than those treated with vehicle. Interestingly, compared with mice treated with oseltamivir (a current treatment for influenza), the majority of NHC-treated mice had no detectable virus in the central nervous system. Due to low viral transmission between mice, the researchers also tested whether NHC affected viral spread using a guinea pig model infected with NL/09 influenza virus. Following infection, viral spread in animals treated with 100 mg/kg NHC was delayed by one day; in animals treated with 400 mg/kg NHC, transmission was detected only eight days post-infection and was very low.
Together, the results of this study demonstrate that oral NHC is effective against influenza and influenza-like viruses in preclinical animal models.
Have you been using Lifeline cell systems in your research? If so, we want to know! Reach out to us and your published study could be the next to be featured here on the blog!