Lysozyme Protects Against Severe Acute Respiratory Syndrome Coronavirus 2 Infection and Inflammation in Human Corneal Epithelial Cells

PURPOSE: The purpose of this study was to investigate the effects of lysozyme, an antimicrobial enzyme found in tears that protects the eye against pathogens, on pseudotyped severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection through corneal epithelial cells. METHODS: The expression of the angiotensin-converting enzyme 2 (ACE2) and transmembrane serine protease (TMPRSS2) in human corneal epithelial cells (HCECs) was measured by RT-PCR and Western blotting. The altered expression of the pro-inflammatory molecules induced by spike protein and lysozyme was analyzed by RT-PCR. Cell toxicity was tested by CCK8 assay. The cell entry of SAR-CoV-2 in HCECs and primary rabbit corneal epithelial cells (RbCECs) was detected by luciferase assay. RESULTS: ACE2 and TMPRSS2 were highly expressed in HCECs. The spike proteins of SARS-CoV-2 stimulated a robust inflammatory response in HCECs, characterized by increased secretion of pro-inflammatory molecules, including IL-6, TNF-α, iNOS, and MCP-1, and pretreatment with lysozyme in HCECs markedly decreased the production of proinflammatory molecules induced by spike proteins. In addition, the inflammatory cytokine TNF-α enhanced the entry of SARS-CoV-2 into HCECs, which can be mitigated by pretreatment with lysozyme. CONCLUSIONS: In this study, we analyzed the susceptibility of human corneal epithelial cells to SARS-CoV-2 infection and suggested the protective effects of lysozyme on SARS-CoV-2 infection.