SARS-CoV-2 beta variant replicates better, induces higher immune response in conjunctiva
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A study conducted on tissue samples and cultured cells demonstrated that SARS-CoV-2 can efficiently infect human conjunctival epithelial cells, eliciting innate immune response.
“We were also able to demonstrate that the beta variant of concern replicates more and induces a much higher inflammatory response,” Ashok Kumar, PhD, told Healio/OSN.
Kumar, an associate professor of ophthalmology, visual and anatomical sciences at Wayne State University School of Medicine, Detroit, has a specific research interest in infectious diseases that affect the eye. In a previous paper, he and his group were able to identify the presence of SARS-CoV-2 RNA as well as spike and envelope proteins in postmortem corneal and scleral tissue of COVID-19 donors. In this more recent study, similar findings were reported in postmortem conjunctival tissues. In addition, the mechanisms and timing of viral entry and replication, as well as the immune response to the virus, were clarified in a cultured human conjunctival epithelial cells (hCECs) model.
“This study was a collaborative work between my lab at Wayne State University, Cedars-Sinai Medical Center in Los Angeles and University of California, Los Angeles. At Cedars-Sinai, Dr. Alexander Ljubimov, an expert in ocular surface diseases and cell cultures, harvested the conjunctival tissue from healthy donors and cultured the cells in a dish. At UCLA, Dr. Vaithi Arumugaswami performed the infection studies in BSL-3 high-containment facility where the cells were infected with a parental strain of SARS-CoV-2 (the original Wuhan virus) and with the beta variant of concern (the so-called South African variant). Samples were then sent to us, and we performed molecular biology analyses,” Kumar said.
Viral entry, replication, immune response
The study demonstrated that both the parental strain and beta variant were able to infect the hCECs, possibly by binding to the ACE2 and TMPRSS2 receptors, well known as entry receptors for SARS-CoV-2. In addition, three other receptors — CD147, Axl and neuropilin-1 — implicated in viral entry, including SARS-CoV-2, were also found to be expressed in this experimental model.
“Distinct expression of all these receptors was detected in most cultured hCECs, as well as in the conjunctival epithelium ex vivo. The presence of permissive viral entry receptors in the conjunctiva potentially enables the virus to use the eye as a site of replication and dissemination to other organs, as seen with other RNA viruses,” Kumar said.
Once the cells were infected, the innate immune response was triggered, leading to production of cytokines, chemokines, interferons and interferon-stimulated genes.
Two further interesting observations were made. First was that virus replication, the expression of receptor genes and the immune response have an early peak at 24 hours and then decline. This trend was consistent in the cells derived from three different donor samples.
“SARS-CoV-2 infects the conjunctiva but does not kill the cells. The conjunctiva as well as the cornea seem to be able to mount antiviral response to the virus, and that could be the reason why we don’t see a much higher increase beyond 24 hours. Very different is the behavior of the virus in the lungs, where cells are killed in a very high number. The lungs may be the real primary target of SARS-CoV-2,” Kumar said.
Comparing the different reaction of corneal and lung epithelial cells to SARS-CoV-2 infection will be the objective of further studies.
The higher power of the beta variant
Another important highlight was that the beta variant replicates more and induces a higher inflammatory response as compared with the parental virus.
“This indicates that this variant is more contagious, and we expect to find an even higher infectivity with the delta, which we are going to look at. Down the line there are so many variants, with so many mutations in each one of them, and the question is whether they are becoming more and more infectious,” Kumar said.
The emergence of new variant strains of SARS-CoV-2 — more transmissible, more aggressive and potentially resistant to vaccines — is a concern and may threaten the progress made so far thanks to mass vaccination, he said.
In an ongoing study, a large number of samples, mainly corneal samples, have been collected for screening from eye banks in seven U.S. states.
“So far, we have analyzed over 600 samples, and those which were positive for SARS-CoV-2 are being analyzed by next-generation sequencing. This would indicate whether a specific variant is prevalent in the ocular tissue and to clarify the mechanisms underlying the increased inflammatory response to these variants of concern,” Kumar said.
Further research may also help find answers to the key questions of whether and to what extent SARS-CoV-2 can enter the system through the eye and whether ocular involvement is secondary to systemic infection.
“Identifying organs and cell types permissive to viral entry and replication could help us to develop preventative or therapeutic strategies against SARS-CoV-2 transmission,” Kumar said.
For more information:
Ashok Kumar, PhD, can be reached at Department of Ophthalmology, Visual and Anatomical Sciences, Wayne State University, 540 E. Canfield Ave., 8374 Scott Hall, Detroit, MI 48201; email: akuma@med.wayne.edu.
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Singh S, et al. Ocul Surf. 2021;doi:10.1016/j.jtos.2021.09.007.
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