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INTRODUCTION: Seasonal human coronaviruses (HCoV) are endemic to the human population, regularly infecting and reinfecting humans while typically causing asymptomatic to mild respiratory infections. The human coronavirus OC43 (HCoV-OC43) is one of the most common causes of the common cold but can lead to fatal pneumonia in children and the elderly. However, no vaccines or antiviral treatments are available against this virus. Animal models available to study HCoV-OC43 and test antiviral counter measures do not accurately recapitulate the respiratory symptoms and physiopathology observed in humans. These limitations impede our understanding of HCoV-OC43 pathogenesis and the development of efficient antiviral therapies or vaccines. Objective: Animal models are crucial for enhancing our understanding of HCoV-OC43 pathophysiology and pathogenesis, and to enable the development of vaccines or therapeutics. In this study, we tested the susceptibility of various mice models to HCoV-OC43 infection and identified type-I interferon signaling as an immune barrier that restricts HCoV-OC43 infection in mice. Utilizing mice defective for type-I interferon signaling (IFNAR -/ -mice), we established virological and histopathological readouts that could assist in identifying avenues for this model to be used for vaccines and therapeutic evaluations. Methods: C57BL/6, IFNAR -/-, and IFNAR -/- mice treated with anti-IFN-λ (antibodies blocking type-III Interferon cytokines) were infected with different doses of HCoV-OC43. Nasal passages and lung tissues were analyzed at different time points during the course of the infection. Focus forming assay and RT-qPCR were utilized to determine viral titers and loads in the lung, respectively. Tissues were stained with Hematoxylin and eosin for histopathological evaluation and immunohistochemistry was performed for quantification of HCoV-OC43 spike protein via image analysis. Whole slide images were generated using a Vectra PolarisTM whole slide scanner and digital analysis with area quantification (AQ) was completed using HALOTM v3.5.3.2577 The region of interests included the olfactory and respiratory epithelium of the nasal cavity. Algorithms to quantify the spike protein were designed specifically for each slide. Signal intensity was selected by pixel pigmentation and using the real-time tuning function in HALOTM v3.5.3.2577 allowing capture of accurate biological signal. Statistical analysis was conducted using GraphPad PrismTM 9.5.1. Results: IFNAR -/- mice intranasally inoculated with HCoV-OC43 displayed greater viral antigen in the olfactory epithelium compared to C57BL/6 mice at three-and-five days post infection. IFNAR -/- mice also displayed mild histopathological manifestations in the respiratory epithelium compared to infected C57BL/6 wild-type mice. Minor histological characteristics seen in the IFNAR -/- mice were characterized by mild rhinitis with neutrophilic and mononuclear influx including edema at the level of the respiratory epithelium, scarce numbers of denuded olfactory epithelium, and mild squamous metaplasia at the level of the respiratory epithelium. No differences in lung viral loads were observed between the two models throughout the infection course, suggesting that additional immune barriers or absence of specific human factors prevent viral dissemination to the lower respiratory tract in mice. Interestingly, treatment of IFNAR -/- mice with antibodies targeting type III interferon cytokines increased viral replication in the olfactory epithelium and extended viral dissemination to the respiratory epithelium of the nasal cavity compared to control IFNAR -/- mice. Altogether, our findings indicate that IFNAR -/- mice represent a potential mouse model of HCoV-OC43 infection, albeit viral replication is restricted to the nasal cavity. More research is needed to identify additional immune barriers, including type III interferon signaling, restricting viral replication in the mouse respiratory epithelium. Conclusion: Combining virological, molecular biology, and histopathological techniques, our study identify type I and III interferon signaling as restriction mechanisms of HCoV-OC43 replication in the mouse nasal cavity. Our work highlights IFNAR -/- mice as a potential model to study early HCoV-OC43 pathogenesis, and open avenues for developing advanced mouse models enabling the evaluation of vaccine candidates. / 2026-02-28T00:00:00Z

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