Purpose: SARS-CoV-2 RNA has been detected in ocular tissues, but their susceptibility to SARS-CoV-2 infection is unclear. Here, we tested whether SARS-CoV-2 can infect human conjunctival epithelial cells (hCECs) and induce innate immune response.
Methods: Conjunctival tissue from COVID-19 donors was used to detect SARS-CoV-2 spike and envelope proteins. Primary hCECs isolated from cadaver eyes were infected with the parental SARS-CoV-2 and its beta variant of concern (VOC). Viral genome copy number, and expression of viral entry receptors, TLRs, interferons, and innate immune response genes were determined by qPCR. Viral entry receptors were examined in hCECs and tissue sections by immunostaining. Spike protein was detected in the cell culture supernatant by dot blot.
Results: Spike and envelope proteins were found in conjunctiva from COVID-19 patients. SARS-CoV-2 infected hCECs showed high viral copy numbers at 24-72h post-infection; spike protein levels were the highest at 24hpi. Viral entry receptors ACE2, TMPRSS2, CD147, Axl, and NRP1 were detected in conjunctival tissue and hCECs. SARS-CoV-2 infection-induced receptor gene expression peaked at early time points post-infection, but gene expression of most TLRs peaked at 48 or 72hpi. SARS-CoV-2 infected hCECs showed higher expression of genes regulating antiviral response, RIG-I, interferons (α, β, & λ), ISG15 & OAS2, cytokines (IL6, IL1β, TNFα), and chemokines (CXCL10, CCL5). Compared to the parental strain, beta VOC induced increased viral copy number and innate response in hCECs.
Conclusions: Conjunctival epithelial cells are susceptible to SARS-CoV-2 infection. Beta VOC is more infectious than the parental strain and evokes a higher antiviral and inflammatory response.
Keywords: COVID-19; Conjunctiva; Eye; Inflammation; Ocular surface; SARS-CoV-2; Viral entry receptors.
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