Inhibitory effect of anti-NA antisera against 3 virus concentrations (100, 25, and 10 TCID50) as determined by virus replication inhibition assay.
Anti-H5N1 NA antisera modestly inhibit replication of reverse genetic (rg) virus carrying homologous NA and show moderate level of antibody titers that cross inhibit the H1N1pdm virus. On the other hand, anti-H1N1 NA antisera well inhibit replication of the H1N1pdm virus, but not cross inhibit rgH5N1 virus. Both kinds of anti-NA antisera do not inhibit rgPR8 virus and H3N2 virus. No significant difference in anti-NA antibody titers is found between pooled mouse sera collected at 4 weeks and 6 weeks p.i. (Mann-Whitney U test, p > 0.05). The geometric mean antibody titers are calculated. The error bars indicate standard deviations of 2 independent experiments for each lot of the test sera.