Inhibitory activity of neutralizing anti-CHIKV MAbs.

Neutralizing activity was determined by FRNT on Vero or NIH 3T3 cells with increasing concentrations of purified MAbs and 100 FFU of the indicated CHIKV strains corresponding to different genotypes (CHIKV-LR, East, Central, and South African; CHIKV-RSUI, Asian and, IbH35, West African). The data were derived from three independent experiments performed in duplicate or triplicate. The inhibitory concentrations of MAb that reduced infected foci by 50% (EC50) and 90% (EC90) were calculated by nonlinear regression analysis and are expressed as ng/ml of antibody. In parenthesis, immediately below the EC50 and EC90 values, are confidence intervals (CI). Bold indicates that the EC50 or EC90 value was greater than the highest concentration (10,000 ng/ml) of MAb used. Bold and italicized indicates an EC50 or EC90 value of less than or equal to 10 ng/ml, which reflects a highly neutralizing MAb for a given cell type or virus strain. N.D. indicates not determined. Of note, NIH 3T3 cells are less permissive than Vero cells (1 FFU on NIH 3T3 cells = 35 FFU on Vero cells).