Investigating temperature-dependent differences in human coronavirus OC43 replication and Type I interferon signalling in human cells

Human coronaviruses (HCoVs) are widespread respiratory pathogens that generally cause mild upper respiratory tract (URT) infections, unlike epidemic coronaviruses such as SARS-CoV, MERS-CoV and SARS-CoV-2, which more often replicate in the lower respiratory tract (LRT) and cause severe disease. A physiological temperature gradient exists in the airway, with 33 °C in the URT and 37 °C in the LRT. I tested whether HCoV-OC43 confinement to the URT reflects temperature-dependent regulation of type I interferon. I combined multi-cycle growth assays across human cell infection models, transcriptomics in primary nasal epithelial cells, stimulation of pattern-recognition receptors, IFNα pretreatment and JAK/STAT inhibition, and targeted knockouts. Across multiple cell types, HCoV-OC43 replicated more efficiently at 33 °C than at 37 °C. Replication was sensitive to IFNα at both temperatures, yet induction of interferon-stimulated genes was reduced at 33 °C, resulting in a weaker antiviral state. Cytokine profiling following stimuli revealed that secretion of cytokines was generally stronger at 33 °C. PRR stimulation revealed temperature sensitivity of RIG-I signalling, with stronger ISG induction and MAPK or STAT phosphorylation at 37 °C and attenuated responses at 33 °C. In contrast, MDA5/TLR3 pathways and direct IFNAR signalling were relatively stable across temperatures. In A549 knockouts, loss of RIG-I, MDA5, or MAVS increased replication, however, only MAVS deficiency attenuated the temperature-dependent replication difference, indicating that MAVS is a major contributor to antiviral restriction at 37 °C while additional temperature-sensitive mechanisms remain operative. These data support a dual mechanism for HCoV-OC43 upper-airway tropism, where cooler temperatures promote replication and attenuate MAVS-linked antiviral programs. While MAVS emerges as a critical adaptor in this process, further research is needed to define its interplay with downstream effectors and to assess how such temperature-sensitive innate responses shape coronavirus tissue tropism more broadly.