SARS-CoV-2 can efficiently infect human conjunctival epithelial cells (hCECs) and elicit an innate antiviral response, according to the results of a recent study published in The Ocular Surface.
“Although the SARS-CoV-2 RNA has been detected in the ocular surface tissues, there is an ongoing debate on the direct role of the ocular surface as a route of virus transmission,” the study explains.
The investigators tested whether SARS-CoV-2 can infect hCECs and elicit innate antiviral and inflammatory response and evaluated differential susceptibility of the cells to parental and emerging variants of concerns (VOCs) of SARS-CoV-2.
The team obtained conjunctival tissues from donor eyes of individuals who were healthy, and those who had COVID-19. These were immunostained for viral proteins and viral entry receptors.
Primary hCECs were isolated from the eyes of human cadavers. The cadaver-derived hCECs and ex vivo tissues were immunostained for the viral entry receptors and cell markers. These cells were also cultured and infected with live SARS-CoV-2. Quantitative polymerase chain reaction analysis was used to evaluate innate immune response, and dot blot of cell culture supernatant was used to detect spike protein.
The investigators found spike and envelope proteins in conjunctiva from COVID-19 patients. They also demonstrated that SARS-CoV-2 infected hCECs had high viral copy numbers between 24 and 72 hours post-infection (hpi), with spike protein levels being the highest at 24 hpi.
The team confirmed that the viral entry receptors ACE2, TMPRSS2, CD147, Axl, and NRP1 were detected in conjunctival tissue and hCECs. They found that SARS-CoV-2 infection induced receptor expression at early time points following infection and that gene expression of most toll-like receptors, indicative of an innate immune response, peaked at 48 or 72 hpi. The investigators also found higher expression of genes regulating antiviral response, RIG-I, interferons (α, β, and λ) interferon-stimulated gene 15, oligoadenylate synthetase 2, cytokines (IL-6, IL1β, and TNFα), and chemokines (CXCL10 and CCL5) in SARS-CoV-2 infected hCECs vs control cells. They also discovered that the beta VOC induced increased viral copy number and innate response in hCECs relative to the parental strain.
“[O]ur study is the first to report that the beta variant of SARS-CoV-2 has increased tropism towards hCECs,” according to investigators. “[F]urther studies are needed to 1) evaluate the differential susceptibility of ocular surface parts including the cornea and conjunctiva to other more prevalent VOCs such as delta variant, and 2) to determine the mechanisms underlying increased inflammatory response during VOCs infection.”
Singh S, Garcia G, Shah R, et al. SARS-CoV-2 and its beta variant of concern infect human conjunctival epithelial cells and induce differential antiviral innate immune response Published online September 25, 2021. Ocul Surf. 2021;S1542-0124(21)00106-3. doi:10.1016/j.jtos.2021.09.007