Tropism, replication competence, and innate responses of the coronavirus SARS-CoV-2 in human respiratory tract and conjunctiva: an analysis in ex-vivo and in-vitro cultures
Authors: Hui KPY et al
Journal/ Pre-Print: Lancet Respiratory Medicine
Tags: Virology; Immunology
1. Unlike SARS-CoV, SARS-CoV-2 infects and replicates in human conjunctiva tissue, suggesting fomite transmission to the eyes is possible.
2. In bronchial tissue, SARS-CoV-2 exhibits similar dynamics to MERS-CoV and replicates more efficiently than SARS-CoV.
3. Infection with SARS-CoV-2 results in modest pro-inflammatory gene induction in comparison with H1N1 and H5N1 influenzas, in primary human airway epithelial cells, macrophages and Caco-2 cells.
Transmissibility and pathogenesis of SARS-CoV-2 remains poorly understood. Hui et al aimed to elucidate SARS-CoV-2 infection dynamics and compare with previously studied SARS-CoV, MERS-CoV, H1N1, and H5N1 influenza. Immunohistochemistry (IHC) of ex vivo tissue 96 hours post infection (hpi) revealed comparable tropism between all viruses in the lung and bronchus, with notably higher staining of SARS-CoV-2 in the bronchus. SARS-CoV-2 replication in the bronchus and conjunctiva was greater than SARS-CoV and in the bronchus, comparable to MERS-CoV. Infection with SARS-CoV-2 and SARS-CoV, in comparison with influenza and MERS-CoV, demonstrated lower pro-inflammatory gene expression in airway epithelial, macrophage, and Caco-2 cells. Higher transmissibility of SARS-CoV-2 in comparison with SARS-CoV may be attributable to the above differences in infection dynamics.
Impact for SARS-CoV2/COVID19 research efforts
Understand the immune response to SARS-CoV2/COVID19
qPCR of primary human airway epithelial cells, macrophages and Caco-2 cells revealed the effects of SARS-CoV-2 in comparison with SARS-CoV, MERS-CoV, H1N1, and H5N1 influenza infection on the host inflammatory response
Understand the virology and/or cell biology of SARS-CoV2/COVID19
Immunohistochemistry and ex vivo viral replication assays detail the tropism and replication ability of SARS-CoV-2 in comparison with SARS-CoV, MERS-CoV, H1N1, and H5N1 influenza
Clinical symptoms and pathogenesis of SARS-Cov2/COVID19
Analysis of SARS-CoV-2 infection in different tissues and the influence on the host immune response may explain the difference in infection outcome with SARS-CoV-2 vs other coronaviruses and influenzas
· In vitro study
· Ex vivo cultures
Strengths and limitations of the paper
Novelty: SARS-CoV-2 replicates more readily in the conjunctiva and bronchus vs SARS-CoV. In the bronchus, SARS-CoV-2 replicates at levels comparable to MERS-CoV.
Standing in the field: Finding that SARS-CoV and SARS-CoV-2 replicate comparably in the lung is in disagreement with the previous finding that SARS-CoV-2 replicates more efficiently than SARS-CoV in ex vivo human lung tissue (https://pubmed.ncbi.nlm.nih.gov/32270184/). Additionally, SARS-CoV and SARS-CoV-2 infection previously seen to increase IL-6 expression at 24 hours in ex vivo human lung (https://pubmed.ncbi.nlm.nih.gov/32270184/), whereas no changes in gene expression following SARS-CoV or SARS-CoV-2 noted here in primary airway epithelial cells.
Additionally, there is preliminary evidence to suggest goblet cells do not express ACE2 (https://www.medrxiv.org/content/10.1101/2020.05.08.20092866v1) to enable infection with SARS-CoV-2, contrary to the findings in this paper where SARS-CoV-2 was found in goblet cells.
Appropriate statistics: Yes
Viral model used: SARS-CoV-2 (BetaCoV/Hong Kong/VM20001061/2020); SARS-CoV (HK39849); MERS-CoV (prototype human MERS-CoV EMC strain); HPAI H5N1 virus (A/Hong Kong/483/1997); 2009 H1N1pdm virus (A/Hong Kong/415742/2009). SARS-CoV-2, SARS-CoV and influenza viruses were isolated from infected patients in Hong Kong. MERS-CoV provided by Prof. R. Fouchier, Erasmus University Medical Centre, Rotterdam.
Translatability: Low, may inform of strategies to reduce SARS-CoV-2 transmission. E.g. as found in conjunctiva, emphasis on importance of eye protection in addition to masks, gloves etc. included in PPE scheduling.
· Small n numbers, particularly in inflammatory response assay (n = 5 or 4 in ex vivo cultures, n = 3 in in vitro inflammatory response experiment).
· Pro-inflammatory gene induction only analysed at single time point (24 hpi for airway epithelial cells and macrophages and 48 hpi in Caco-2 cells)
· Nasopharynx not analysed
· IFN gene expression not included in host response qPCR panel