<p>(A) Neutralization of EBOV GP pseudovirus. Neutralizing activity of antisera was determined by incubating 500 pfu of GP<sub>1,2</sub>-pseudotyped virus with dilutions of pooled GP<sub>1,2</sub>-immunized (Blue), sGP-immunized (Red), and empty pCAGGS vector-immunized (black) antisera. Neutralization was measured as decrease in luciferase expression compared to virus-only controls after 48 h. (B) Interference of EBOV GP pseudovirus neutralization by sGP. The ability of sGP to interfere with antibody-dependent neutralization was determined by allowing sGP to compete with GP<sub>1,2</sub> pseudotyped viruses for anti-GP<sub>1,2</sub> antibodies. Pooled GP<sub>1,2</sub>-immunized (blue) and sGP-immunized (red) antisera were fixed at the dilution corresponding to 80% neutralization. Antisera was co-incubated with increasing dilutions of His-tagged sGP (solid markers) or His-tagged influenza PR8 HA (open markers), and rescue of infectivity was measured as described in methods.</p
