(A) The ELISA reactivity to NA mAb (HCA-2) in the M1 (from A/PR8 virus) or N1 NA (from A/Cal, H1N1 virus) rBV-infected insect cells. NA expression on the insect cells infected with M1 or N1 rBVs was determined with anti-NA mAb (HCA-2) by ELISA. (B) The reactivity of N1 VLP to NA mAb (HCA-2) by ELISA. (C) The expression of NA protein on VLPs was determined by western blot probed with rabbit HCA-2 mAb. Influenza N1 VLP (20, 10, 5 μg), inactivated A/Cal (H1N1) virus (10, 5 μg), M2e5x VLP (5 μg) were loaded. (D) Size distribution of N1 VLP as measured by Malvern Zetasizer with dynamic light scattering (DLS). (E) Neuraminidase activity by an enzyme-linked lectin assay. Statistical significance was determined by using one-way ANOVA. Data are representative of individual animal out of two independent experiments. Error bars indicate the means ± SEM. ***, p<0.001.