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Leaderless FMDV O does not establish a persistent infection in multilayered cells derived from bovine dorsal soft palate
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International audience. A subclinical infection may occur if a virus can counteract the host immune response. For foot-and mouth disease virus (FMDV), the major viral protein known to be involved in host innate response evasion during acute infection is the leader protease Lpro. Indeed it has been previously shown that the deletion of the Lpro-coding region results in highly attenuated viruses in vivo. If both wild type and leaderless viruses replicate at the primary site of infection in the nasopharynx, the leader-deleted viruses failed to generalize and to cause viremia with subsequent disease. It was however not explored if the leaderless FMDV could establish a persistent infection. Here we have investigated if a recombinant leaderless FMDV O could persist in-vitro in multilayer cells from bovine dorsal soft palate (DSP) grown at the air-liquid interface (ALI). In this assay, DSP cells were cultured on inserts for five weeks, then inoculated with either recombinant wildtype FMDV O/FRA/1/2001 or its leaderless derivative O FRA delta Lpro, or a placebo. The upper multilayer was washed with culture medium 6, 12, 24 and 48h post-infection and thereafter each two/three days until 35dpi. Wash medium was analysed to detect infectious FMDV and viral RNA. Live wt virus was isolated from supernatants of 5/6 cultures while no leaderless live virus had been detected after 48h post-inoculation of DSP-ALI. These results were confirmed by viral titration. Likewise, leaderless viral RNA decreased from 7dpi until 28dpi to the point of becoming undetectable at 35dpi. Proteogenomics analysis will complete these data.Overall, our results show that the leaderless FMDV O virus cannot establish a prolonged nor persistent infection in DSP-ALI cells.In a companion study presented at the conference by Litz et al., O FRA leaderless was also found to be strongly attenuated in cattle and unable to establish persistent infection.
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