Fig 4.

Combined effect of human A33 and B5 against EV virion and the impact of anti-A33 Ab in smallpox-vaccinated humans. (A) VACV EV neutralization activity of the fully human MAbs against B5 (h102) and A33 (VV22) at 20, 10, or 1 μg/ml of each MAb in the absence or presence of 1% complement. (B) Irrelevant human IgG1 MAb and EV (anti-DNP) at 40, 20, or 2 μg/ml were negative controls with or without complement. Data are represented as plaque numbers. The dashed line indicates 50% of the plaque numbers of VACV EV with or without complement. (C) VACV EV neutralization activity (%) of plasma from donors (b, c, e, g, and i) in the presence of complement and after the blockade of anti-A33 or anti-B5/A33 Abs with 10 μg of rA33 or rB5/rA33 proteins. *, P < 0.05. The dashed line indicates 50% of neutralization activity. Error bars indicate SEM under each condition. All data are representative of two independent experiments.