Figure 3.

Activities and protectiveness of M2e-specific antibodies induced by the PR8 Ca2 M2 virus. (A) M2e-specific antibodies are non-neutralizing but engage in Fc-mediated effector functions. Microneutralization (MN) assay was performed using a recombinant H3N2 virus expressing the heterosubtypic HA and NA in the PR8 backbone. Mouse sera generated by sublethal infection with the same H3N2 virus was used as positive controls. HA assay was used as the readout for the MN assay. ADCC reporter assay was performed using transfected 293T cells transiently expressing the PR8 M2. Fold induction of the reporter signals from the sera over those from the blank were analyzed. Statistical difference was determined using one-way ANOVA corrected for multiple comparisons using Dunnett’s test (ns, not significant; *, p < 0.05; **, p < 0.01; ***, p < 0.001; ****, p < 0.0001). (B) Passive serum transfer and virus challenge study. Two hundred microliters of pooled sera from each group were transferred into naïve mice intraperitoneally (IP). Mice were challenged with the X-31 virus at a dose of 5x LD₅₀ two hours after serum transfer. Weight loss and survival were monitored for two weeks.