Figure 2.

Neutralizing capacity of anti–chikungunya virus (CHIKV) immunoglobulin G3 (IgG3) antibodies. A, Visualization of CHIKV by immunofluorescence in infected cultures after seroneutralization. Virus samples were preincubated with patients’ plasma collected at median 10 d post–illness onset (PIO) from early and late IgG3 groups before being added to the cells. Noninfected (mock) or virus samples preincubated with healthy donor plasma were used as controls. Analysis was performed at 6 h postinfection. Images were captured with 60× magnification. Scale bar: 50 μm. Representative microscopic images per treatment condition are illustrated. B, In vitro neutralizing activity against CHIKV from plasma samples of early and late IgG3 responders. Plasma samples (median, 10 d PIO) were tested in triplicates at different dilutions. Healthy plasma was used as a control and performed in the same conditions. Dilution at 1:100 is shown. Results are presented as mean ± SD of percentage control infection. Data are representative of 3 independent experiments. Statistical significance was measured using Mann–Whitney U test. *P < .05. **P < .01.