CHIKV-Infected Human Dermal Fibroblasts Mount an IFNβ Transcriptional Response Independent of TBK1/IKKε Signaling...

Chikungunya virus (CHIKV) is an alphavirus that infects dermal fibroblasts as a primary target cell during natural mosquito-borne transmission. While primary human dermal fibroblasts (hDFs) have been implicated as a key source of type I interferon (IFN-I) during CHIKV infection, the dynamics of this response and its sufficiency for antiviral protection remain incompletely understood. Here, we systematically characterize in vitro CHIKV infection of primary hDFs, evaluating the effects of single-passage viral stock origin (mammalian- vs. mosquito-propagated), donor variability, and multiplicity of infection (MOI) on infection kinetics and innate immune induction. We demonstrate that hDFs support high-titered CHIKV replication at both MOI 1 and 0.01, resulting in universal cell death by 72 hpi despite robust IFNβ transcript induction-reaching up to ~2800-fold over mock-and secretion of pro-inflammatory cytokines, including IFNα2, TNFα, IL-1β, and IL-8. Notably, IFNβ protein levels remained below 10 pg/mL under all infection conditions, revealing a disconnect between transcriptional and translational responses, suggesting CHIKV-mediated translational suppression. Pharmacological inhibition of TBK1/IKKε via amlexanox did not suppress IFNβ transcript induction at any tested concentration, suggesting that canonical PRR signaling through this node-including both RIG-I/MAVS and TLR3/TRIF pathways-is not the major driver of the observed transcriptional response. In contrast, co-inoculation with exogenous IFNβ as low as 20 pg/mL activated IFNAR signaling, robustly upregulated interferon-stimulated genes (ISGs), and fully rescued hDFs from otherwise lethal infection. Together, these findings demonstrate that CHIKV-infected hDFs mount a transcriptionally robust but translationally insufficient innate immune response and that the transcriptional response appears to operate independently of TBK1/IKKε. These results have direct implications for understanding how the skin microenvironment may modulate early CHIKV pathogenesis and suggest that paracrine IFNβ signaling from neighboring cell types may be critical for fibroblast survival during natural infection.