Efficient production of activated HA protein of influenza virus by WSSV ie1 promoter in baculovirus. (A) Immunofluorescence assays with different recombinant baculovirus infected SF9 cells. Cells were fixed 3 days post-infection and subjected to antibody staining. 3D4 and 8B6 are H5-specific monoclonal antibodies. Anti-VSVG is anti-VSV G protein antibody. (B) Hemagglutination assays. Every 25 μl of baculovirus at a titer of 1010 PFU/ml was loaded into the standard hemagglutination assay. Data were collected from 4 parallel assays. (C) One-step growth curves of baculoviruses under three different promoters in SF9 cells. Each data point represents the mean value of four individual infections. SF9 cells were infected by individual viruses with a MOI of 0.5 PFU/cell. (D) HA contents of baculoviruses under three different promoters during infection. Data, shown in mean + SD, were collected from 4 parallel assays.