Neutralization and binding activity of F005-126 against mutant Aic68/N285Y. (A) Neutralization activity of F005-126 against an escape mutant, Aic68N285Y, was weaker than that against the wild-type Aic68 strain. (B) FCM analyses of the cells expressing Aic68HA/wild-type and a mutant Aic68HA/N285Y were performed. FCM signals for mock transfection (gray filled), wild-type HA-expressing cells (blue), and mutant HA-expressing cells (red) are shown. F045-092, F003-137, and F035-015 recognize the HA head region (24, 34). Binding activity of F005-126 to Aic68HA/N285Y was weaker than that to wild-type HA.