Figure 1.

Antibody (Ab) profiles of chikungunya virus (CHIKV)–infected patients. A, Virus-specific immunoglobulin M (IgM) and immunoglobulin G (IgG) antibody titers in plasma samples (n = 30) at a dilution of 1:2000 were determined by enzyme-linked immunosorbent assay (ELISA) using purified CHIKV virions. B, Detection of CHIKV by plasma from CHIKV-infected patients. HEK 293T cells were infected with CHIKV (SGP11) at a multiplicity of infection of 10, fixed at 6 h postinfection, and stained with 2 representative patients’ plasma at 2–3 months post–illness onset (PIO) using a dilution of 1:500. Healthy plasma was used as a control. CHIKV antigen was detected by antihuman IgG antibody conjugated to Alexa Fluor 488 (green). 4′,6-diamidino-2-phenylindole (DAPI) was used to stain the nucleus. Scale bar: 10 μm. C, Virus-specific IgG isotype titers in plasma samples. Immunoglobulin G1 (IgG1) (□), immunoglobulin G2 (IgG2) (Δ), immunoglobulin G3 (IgG3) (•), or immunoglobulin G4 (IgG4) (⋄) Abs were determined as in (A) using specific secondary antibodies. Each point represents the mean of 30 patients’ samples from the cohort. D, Chikungunya virion–based ELISA was used to determine virus-specific IgG isotype titers in plasma samples (median, 10 d PIO; n = 30) at a dilution of 1:100. Anti-CHIKV IgG1, IgG2, IgG3, or IgG4 Abs were determined using specific secondary Abs. Data are presented as mean ± standard error of the mean (SEM) of 30 patients’ samples and are representative of 2 independent experiments with similar results. E, Profile of IgG3 levels at different times PIO in early (n = 16) and late IgG3 responders (n = 14) according to the pattern of IgG3 titer at median, 10 d PIO. Data are presented as mean ± SEM. Data are representative of 2 independent experiments with similar results. Statistical significance was measured using Mann–Whitney U test. **P < .01. Abbreviation: OD, optical density.