Hemagglutination inhibition assay.

For the assay, 4 HAU of purified plant-produced recombinant hemagglutinin (rHA0) were mixed with 2-fold serial diluted hyperimmune rabbit antiserum (starting at a dilution of 1∶80) generated against various subtypes of viral strains or phosphate buffer saline (PBS) (negative control). Native Swedish H7N7 influenza A virus isolate was used as positive control. Formation of immune complexes was allowed for 30 min at 37°C, before incubation with chicken erythrocytes for 1 h at 4°C.