E.Derm

EIV/63 and EIV/2003 Exhibit Significant Differences in Replication Kinetics, Cell-To-Cell Spread and Susceptibility to Interferon In Vitro

To study the effects of viral evolution on fitness, the researchers performed controlled infections with two H3N8 EIV strains isolated 40 years apart. Mamalian cell lines and horse tracheal explants were infected and viral replication, interferon resistance, cell-to-cell dissemination and tissue damage were assayed. Transcriptomics were used to profile host responses, while image analysis was used to quantify epithelial lesions.

The replication dynamics of EIV/1963 and EIV/2003 were studied in mammalian cells to determine adaptive changes between evolutionarily divergent equine influenza viruses (EIV). Infections were performed in both Madin-Darby Canine Kidney (MDCK) cells and interferon-competent equine dermal fibroblasts (E.Derm), the latter being a more physiologically relevant model. Both viruses replicated with similar kinetics in MDCK cells, however, EIV/2003 reached peak titres three logs greater than EIV/1963 at 48 hpi (Fig. 1B). EIV/2003 also developed considerably larger plaques indicating increased cell to cell dissemination (Fig. 1C, p< 10-17). In E.Derm cells, EIV/2003 always beat EIV/1963 and achieved titers three logs higher from 24 hpi (Fig. 1D, p= 7.98 × 10⁻⁴). EIV/1963 replication was considerably increased following treatment with the JAK1/2 inhibitor, ruxolitinib (p= 0.039) and was comparable to that of EIV/2003. By contrast, ruxolitinib did not impact EIV/2003 replication (p= 0.331). These findings show that the present EIV/2003 lineage is more fit and more resistant to the horse type I interferon response relative to the historical EIV/1963 strain.