Inhibition of headless H/F-mediated membrane fusion by mAb αH-1347. (A, C and D) Syncytium formation assay. Cell-to-cell fusion activity in Vero or Vero-cSLAM cells triggered by co-expression of CDV H-wt or headless H variants with CDV F-wt or CDV F-V447T (A75/17 strain) [ 62 ] in the presence (+) of absence of mAb αH-1347 (-). Representative fields of view of cell-cell fusion induced 24h post-transfection are shown. (B) F-triggering assay. The CDV F-V447T mutant was expressed in Vero cells together with the indicated Hstalk variants. One day post-transfection, the conformation of the FLAG-tagged F-V447T mutant was monitored by probing its reactivity with an anti-F prefusion-specific mAb (4941; green histograms), triggered-specific mAb (3633; red histograms) [ 61 , 63 ]. Secondary antibodies were added at 4°C, and to record quantitative values, mean fluorescence intensities were monitored by flow cytometry. (E) Quantitative fusion assays were performed as described in the legend of Fig 1B in the presence (light grey histograms) or absence (dark grey histograms) of mAb αH-1347. Means ± S.D. of data from three independent experiments performed in duplicates are shown.
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