A and B Hemagglutination activity and negative stain electron microscopy of the H3 rHA proteins. A. The hemagglutination assay was performed in 96-well u-bottom plates. The rHA proteins were assayed in triplicate at an initial concentration of 1 μg/mL loaded in the left-most lane. Two-fold serially dilutions were performed across the plate in PBS, and equal volume 0.5% guinea pig red blood cells added. Endpoints are denoted by dotted lines. B. The rHA proteins were stored at 25°C for 2.5 month at the time of EM analysis. The bar represents 100 nm.