Inhibition of avirulent NDV (La Sota) strain-mediated cell fusion. A) Vero cells infected with NDV and treated by trypsin digestion: a) Uninfected control cells; b) Vero cells infected with NDV and treated with trypsin; c) Infected Vero cells were treated with fucoidan before F protein cleavage, at which point syncytia formation could be inhibited if fucoidan was added; d) Infected Vero cells were treated with fucoidan after F protein cleavage, and fucoidan could not inhibit syncytia formation in this condition. B) Fusion inhibition assay with fucoidan treatment before (BC) and after F protein cleavage (AC). Data are expressed as percent of the number of syncytia and syncytial nuclei compared with the findings in untreated virus-infected control cells. VC, viral control. The data shown are the mean ± SD of triplicate experiments. The asterisks indicate a significant difference between the treatment and viral control (*p<0.05).