Neutralization of Virus Infectivity by Antibodies: Old Problems in New Perspectives
Figure 5
Neutralization potency and efficacy. (a) Potency: conventional neutralization curves (relative infectivity as a function of the logarithmic antibody concentration) for simulated data are shown. The green and red curves describe neutralization with identical potency, that is, IC50 values, although the green curve has a higher slope coefficient. Red, black, and blue curves represent decreasing potencies in that order while having the same slope. Neutralization represented by the grey curve falls between the black and blue in potency but has markedly higher slope coefficient than both. Antigenic heterogeneity reduces the slope coefficient and so does negative cooperativity. Positive cooperativity would raise the slope coefficient. (b) Efficacy: exactly the same simulated data as in (a) are plotted in a log-log plot to illustrate the importance of the persistent fraction (PF) of infectivity after neutralization. The two most potent NAbs from (a) (red and green) are shown to have widely different efficacies: the persistent fraction differs by about three logs. Furthermore, the curves for the less potent NAbs (black and blue) cross the red curve and tend towards a greater efficacy by one or half a log, respectively. The greater slope of the grey curve than of the others is apparent also in this plot but only here is the greater efficacy of the neutralization represented by the grey than by the green curve evident, another case of lower potency and greater efficacy.
