Activation of immune receptor RIG-I protects human differentiated epithelial cells of the upper respiratory tract from SARS-CoV-2

ABSTRACT

SARS-CoV-2 virus has evolved non structural proteins (NSLs) to avoid recogniton by innate immune receptors such as RIG-I which induces an antiviral type I IFN response. A proper type I IFN response is essential for an effective defense against SARS-CoV-2. The aim of this project is the evaluation of the effect of a prophylactic activation of RIG-I by a specific synthetic RNA ligand (5-triphosphate RNA, 3pRNA) to an antiviral state in cells that protects against SARSCoV- 2. We analysed the effect of activation of RIG-I by 3pRNA on SARS-CoV-2 infection in primary upper airway cells. Primary nasal epithelial cells (PNEC) and primary bronchial cells (NHBEC) were cultivated in air-liquid interface and differentiated to cilia bearing epithelial cells. Viral replication was analyzed by plaque assay and qPCR. Furthermore, interferon-stimulated genes and ACE2/TMPRSS2 were determined on the transcriptional level and IP-10 protein was quantified in supernatants by ELISA. Only PNEC in a fully differentiated state could be infected with SARS-CoV-2, while undifferentiated cells were not susceptible to infection with this virus. Upon stimulation with 3pRNA at 6h prior to infection, PNEC produced more than 10.000 pg/ml IP-10. Infection with SARS-CoV-2 significantly decreased the average of 3pRNA-induced IP-10 production. 3pRNA pretreatment of PNEC significantly reduced SARS-CoV-2 replication at 48 h by up to 99,7 % as evaluated by plaque assay and up to 90 % as measured by qPCR. These results demonstrate for the first time that RIG-I activation protects primary fully differentiated epithelial cells against SARS-CoV-2 replication. Our results support the concept that RIG-I-mediated prophylaxis is a promising strategy to mitigate SARS-CoV-2 infection.