Hemagglutination test and hemagglutination inhibition (HI) test

Hemagglutination tests were performed with standard protocols provided by WHO. Briefly, the hemagglutination activity of the purified H7N9 rHA was tested against 1% (v/v) chicken red blood cells (RBCs), and hemagglutination titers were determined as the highest dilution exhibiting complete hemagglutination (Hu et al. 2017). For conducting HI test, 25 μL of 4 chicken erythrocyte hemagglutination units of purified H7N9 rHA was pre-incubated with 25 μL of different dilutions of F3-2 (1 mg/mL) or 1C6B (1 mg/mL) in a well of a V-bottomed plate for 1 h at room temperature. Twenty-five microliters of 1% (v/v) of chicken RBC suspension was then added to the rHA and mAb mixture, gently shaken, and incubated at room temperature for an additional 40 min. PBS was used as a negative control to replace the mAb for mixing with H7N9 rHA and chicken RBC suspension.