FIG. 1.

HAI capacity of ς3-specific MAb 4F2 IgG and Fabs. T3D virions (4 HA units [10¹¹ particles]) were incubated with IgG and Fabs of MAb 4F2, 9BG5, or 5C6 at the concentrations shown at 37°C for 1 h. Human type A erythrocytes were added, and plates were incubated at 4°C overnight. The HAI titer for each antibody was defined as the lowest concentration of antibody capable of inhibiting HA. The experiment was performed in triplicate. Shown is a representative experiment.