FIG. 9.

PAN amounts of H36 Fab fail to inhibit the appearance of low pH-induced conformational changes in the HA1 of PR8 virus bound to fixed MDCK cells monolayers. Virus (200 HAU) was allowed to attach to cells at 4°C and then incubated with 200 nM H36 Fab at 4 or 37°C as indicated. The Fab gave >99% PAN of the virus used here in MDCK cells. After washing, virus-cell complexes were incubated at pH 5 or 7.5 and at 4 or 37°C for 30 min as shown and then probed with IgGs (as shown) specific for the pH-sensitive epitopes of the HA. Binding of antibodies was determined by ELISA. Data are the mean of three experiments, and the bars represent the standard error of the mean. Numbers in parentheses refer to each experimental procedure.