FIG. 1.

Serotype cross-reactive anti-ED3 antibodies are induced after primary dengue infections in humans. (a) Anti-ED3 endpoint titers (EPTs) were determined for all 4 serotypes by direct ELISA against bacterially expressed recombinant ED3. All plasma samples taken 15 to 30 days after defervescence from individuals with primary dengue infections are shown (n = 25). The cutoff levels of seropositivity for each assay are indicated in the symbol key. Assay values below these cutoffs are not depicted, meaning that for some individuals, not all 4 titers are shown. Twenty-five plasma samples from individuals with primary infections (P1 to P25) are shown below the x axis. The current infecting serotype (Den1 [D1] to Den4 [D4]) as determined by PCR is shown in parentheses below the plasma sample. (b) Competition ELISA for an individual with primary Den1 infection. The anti-ED3(1) and anti-ED3(2) responses, for which ED3(1) and ED3(2) are coated on the ELISA plate, respectively, are shown. The percent maximum OD₄₀₅ is shown on the y axes. Neg, negative. (c) Competition assay for an individual with primary Den2 infection. The anti-ED3(2) and anti-ED3(4) responses are shown.