C to F Binding of C179 (C), or antibodies present in AAV-HA (D), AAV-cHA (E) or WIV (F) pooled pre-challenge sera (n = 18 mice per group) to Cal/7/9 or PR8 virus after incubation of the virions at pH = 7.2, 5.8, 5.4, 5.0, 4.4 or 4.4+DTT to induce conformational changes in HA or remove the HA1 subdomain. Mean ± SD (n = 3, in technical triplicates). Statistical significance between pH = 7.2 and other conditions was determined using Kruskal-Wallis test with Dunn's multiple comparison testing (*p<0.05, **p<0.01). 