Immunohistochemical Study of SARS-CoV-2 Viral Entry Factors in the Cornea and Ocular Surface

To confirm the ocular tropism of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) by evaluating the expression of viral entry factors in human ocular tissues using immunohistochemistry.

Fresh donor corneas and primary explant cultures of corneal, limbal, and conjunctival epithelial cells were evaluated for the expression of viral entry factors. Using immunohistochemistry, the samples were tested for the expression of angiotension-converting enzyme 2 (ACE2), dendritic cell-specific intracellular adhesion molecule 3-grabbing nonintegrin (DC-SIGN), DC-SIGN-related protein (DC-SIGNR), and transmembrane serine protease 2 (TMPRSS2).

In total, 5 donor corneas were evaluated for the expression of viral entry factors. In all specimens, both ACE2 and TMPRSS2 were expressed throughout the surface epithelium (corneal, limbal, and conjunctival) and corneal endothelium. In corneal stromal cells, ACE2 was sporadically expressed, whereas TMPRSS2 was absent. DC-SIGN/DC-SIGNR expression varied between donor specimens. Four specimens expressed DC-SIGN/DC-SIGNR in a similar distribution to ACE2, but 1 specimen from a young donor showed no expression of DC-SIGN/DC-SIGNR. ACE2, TMPRSS2, and DC-SIGN/DC-SIGNR were all expressed in the cultured corneal, limbal, and conjunctival epithelial cells.

Both corneal and conjunctival epithelia express ACE2, DC-SIGN/DC-SIGNR, and TMPRSS2, suggesting that the ocular surface is a potential route for the transmission of SARS-CoV-2. The risk of viral transmission with corneal transplantation cannot be ruled out, given the presence of ACE2 in corneal epithelium and endothelium. Cultured corneal, limbal, and conjunctival epithelial cells mimic the expression of viral entry factors in fresh donor tissue and may be useful for future in vitro SARS-CoV-2 infection studies.