FIG. 2.

Neutralizing activity of hemagglutinin (HA)-specific antibodies in vitro. Inhibition of influenza A virus (IAV) infection by 2E10 (filled squares) and the hybrid IgA (open circles). IAV was pretreated with various concentrations of antibodies (abscissa: final concentrations), and then added to Madin–Darby canine kidney cells. Cells were infected with IAV for 30 min at 37°C and then washed with phosphate-buffered saline. After 7 h of culture, cells were immunostained with antibodies specific for viral nucleoprotein proteins (mAb 4E6). The infected cells were counted under a microscope. Control represents when IAV was added without antibody pretreatment, and the data were expressed as the relative numbers of infected cells compared with the control (ordinate). Data are expressed as means±standard deviation (SD).