Infectious foci formation reduction assay. The following H1N1, H2N2, H3N2, H5N1, H7N2 and H9N2 viruses were . Each viral isolate was titrated to establish working dilution that produces 15-30 foci forming units per well in 96 tissue culture plates. Neutralizing assays were carried out in 96 wells plate using MDCK/SIAT-1 cells. Serial dilutions, 30 mg/ml-0.37 mg/ml, of IgG PN-SIA49 were preincubated for 1 hour at 37uC with the subset of viruses. Following this incubation, 100 ml of the antibody-virus mix was added to the cells and incubated for another hour at 37uC in 5% CO2. At the end of this incubation, the cells were washed twice in PBS and 100 ml of virus growth media containing 2 mg/ml of TPCK treated trypsin was added. Cells were incubated for 12-16 hours at 37uC in 5% CO2 and then washed with PBS, fixed and permeabilized with ice cold methanol/acetic acid (95:5) for 30 min at 220uC. Cells were incubated with anti-NP antibodies (Millipore, Billerica, MA, USA) for 30 minutes at 37u. The cells were then washed and incubated for 30 minutes at 37uC with a mouse HRP-conjugated secondary antibody. True Blue chromogenic substrate (KPL) was used to count the number of foci.