Differential Induction and Signaling of Type I and III Interferons During Infection of Human Nasal Epithelial Cells With the Four Human Parainfluenza Virus Types.

Human parainfluenza viruses (HPIVs) commonly cause croup and lower respiratory tract infections in young children. Despite typically self-limiting with mild symptoms, the innate immune responses to HPIVs remain poorly understood, especially across all four types in human nasal epithelial cells (hNECs), the primary infection site. This study aims to investigate and compare viral replication kinetics and host immune responses in hNECs infected with HPIV types 1 to 4.The hNECs were infected in vitro, and viral replication kinetics, mucociliary function, cell tropism, and innate immune responses were assessed over 72 h. The viral RNA and progeny of HPIV types 1 to 4 were detected by 8 h postinfection (hpi). All HPIV types predominantly targeted ciliated cells of which a significant proportion displayed a unique apical distribution. HPIV-3 generated the highest level of progeny virus and could infect a fraction of nasal goblet cells. RIG-I and MDA5 expression was delayed during HPIV-2 and HPIV-3 infection (24 hpi), whereas HPIV-1 and HPIV-4 induced gradual upregulation from 8 hpi. Minimal upregulation of IFN-α1 mRNA was induced across all HPIV types. Expression of type I IFN-β was generally subdued during the earlier stage of infection (24 to 48 hpi) with the four HPIV types. Notably, IFN-β mRNA expression was significantly elevated for HPIV-1 infection at 48-72 hpi, whereas only a small increase was observed at 72 hpi for the other HPIV types. Although expression of type III IFN-λ1 was similarly delayed for all four HPIV types during the earlier stage of infection, a greater upregulation of IFN-λ1 was detected at 48-72 hpi for all HPIV types (especially HPIV-1) as compared to type I IFN expression. For HPIV-1 and HPIV-4, mRNA expression of CXCL10 and MX1 appeared as early as 8 hpi and gradually increased until 72 hpi. However, for HPIV-2 and HPIV-3, mRNA expression of CXCL10 and MX1 was delayed at 8-16 hpi, but subsequently increased significantly at 24-72 hpi. In comparison, IFITM1 mRNA was expressed at relatively weaker levels for the four HPIV types. In conclusion, all four HPIV types exhibit high infectivity and replicative capacity in hNECs while initially evading interferon responses to varying extents. Their innate immune modulation appears to be type-specific, potentially influencing viral virulence, pathogenesis, and progression of airway disease in high-risk patients.