Tropism, replication competence, and innate immune responses of the coronavirus SARS-CoV-2 in human respiratory tract and conjunctiva: an analysis in ex-vivo and in-vitro cultures

Abstract

Background Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged in December 2019, causing a respiratory disease (coronavirus disease 2019, COVID-19) of varying severity in Wuhan, China, and subsequently leading to a pandemic. The transmissibility and pathogenesis of SARS-CoV-2 remain poorly understood. We evaluate its tissue and cellular tropism in human respiratory tract, conjunctiva, and innate immune responses in comparison with other coronavirus and influenza virus to provide insights into COVID-19 pathogenesis. Methods We isolated SARS-CoV-2 from a patient with confirmed COVID-19, and compared virus tropism and replication competence with SARS-CoV, Middle East respiratory syndrome-associated coronavirus (MERS-CoV), and 2009 pandemic influenza H1N1 (H1N1pdm) in ex-vivo cultures of human bronchus (n=5) and lung (n=4). We assessed extrapulmonary infection using ex-vivo cultures of human conjunctiva (n=3) and in-vitro cultures of human colorectal adenocarcinoma cell lines. Innate immune responses and angiotensin-converting enzyme 2 expression were investigated in human alveolar epithelial cells and macrophages. In-vitro studies included the highly pathogenic avian influenza H5N1 virus (H5N1) and mock-infected cells as controls.Findings SARS-CoV-2 infected ciliated, mucus-secreting, and club cells of bronchial epithelium, type 1 pneumocytes in the lung, and the conjunctival mucosa. In the bronchus, SARS-CoV-2 replication competence was similar to MERS-CoV, and higher than SARS-CoV, but lower than H1N1pdm. In the lung, SARS-CoV-2 replication was similar to SARS-CoV and H1N1pdm, but was lower than MERS-CoV. In conjunctiva, SARS-CoV-2 replication was greater than SARS-CoV. SARS-CoV-2 was a less potent inducer of proinflammatory cytokines than H5N1, H1N1pdm, or MERS-CoV. InterpretationThe conjunctival epithelium and conducting airways appear to be potential portals of infection for SARS-CoV-2. Both SARS-CoV and SARS-CoV-2 replicated similarly in the alveolar epithelium; SARS-CoV-2 replicated more extensively in the bronchus than SARS-CoV. These findings provide important insights into the transmissibility and pathogenesis of SARS-CoV-2 infection and differences with other respiratory pathogens.

Rapid endothelial infection, endothelialitis and vascular damage characterise SARS-CoV-2 infection in a human lung-on-chip model

“…Similar numbers of viral genome copy numbers have been reported for infections of alveolar epithelial cell monoculture 15 and are modest in comparison to airway epithelial cells and Vero E6 cells 27 . Nevertheless, SARS-CoV-2 appears to disseminate rapidly from the epithelial to the endothelial layer.…”

“…These suggest that the lung microvasculature plays a key role in COVID-19 pathogenesis 13 , yet most in vitro studies have focused on monocultures of upper airway respiratory cells. In studies with alveolar epithelial cells, SARS-CoV-2 has been shown to replicate poorly both in the A549 lung adenocarcinoma cell line 14 and in primary alveolar epithelial cells ex vivo 15 and has been reported to be unable to infect primary microvascular endothelial cells 16 , which are at odds with the reported medical literature. There is therefore an urgent need for a better understanding of the pathogenesis of SARS-CoV-2 in alveolar epithelial cells and in a more realistic model of the alveolar space that is vascularized.…”

Age-dependent progression of SARS-CoV-2 infection in Syrian hamsters

“…Furthermore, we show that, using in situ hybridization, viral RNA was detectable in bronchial epithelial cells, type I and type II alveolar epithelial cells, and macrophages. All these cell types are potential targets of SARS-CoV-2 in human lung tissue; hence, infection of hamsters of different ages seems to closely reflect what has been reported for human patients 25,30 . In contrast to SARS-CoV-2 titers, histopathological changes differed markedly between young and aged Syrian hamsters over time: younger animals launched more severe reactions at early time points after infection, while lesions and inflammation in the lungs became more pronounced and widespread at later time points in the elderly.…”

Molecular Interactions of Fullerene-Based Derivatives and SARS-CoV-2

“…The spike protein-receptor interaction is the primary determinant for a coronavirus to infect a host species and also governs the tissue tropism of the virus [38]. On the other hand, the zinc metallopeptidase ACE2 has been identi ed as the main entrance (receptor) for coronavirus into the cells [39].…”