Figure. Neutralization of avian influenza virus A (H5N1) by intravenous immunoglobulin (IVIg) preparations measured by percentage reduction in plaque number (A) and plaque size (B). Monolayers of MDCK cells were infected with virus and overlaid with agar containing various concentrations of IVIg. After 2 days, plaques were detected by staining with crystal violet. Shown is a sample of viral plaques with agar overlay containing different dilutions (1:50–1:800) of Human Immunoglobulin, pH 4.0, (Harbin Sequel Bio-Engineering Pharmaceutical, Harbin, People’s Republic of China) IVIg (C). Data are mean ± SE of 3 experiments.