Age-specific kinetics of neutralizing antibodies and infection enhancement among ≤1 year-old Indian infants

Abstract

Background: Infants born to dengue-immune mothers acquire maternal antibodies to dengue. Maternal antibodies decline over time, making infants susceptible to primary dengue infections. Another important concern is the role of maternal antibodies in causing antibody-dependent enhancement (ADE) during primary infections. In this study, we aimed to investigate the kinetics of dengue virus (DENV)-neutralizing antibodies and infection-enhancing activity in Indian infants.

Methods: Healthy infants at birth (cord blood), and at 3, 6, 9, and 12 months of age (n=32/group) were included in this cross-sectional study. Serum samples were tested for neutralizing antibodies using the foci-reduction neutralization test and enhancing antibodies using the ADE assay against DENV1-4 serotypes.

Results: Neutralizing antibody positivity declined with the increasing age of the infants. Undetectable levels of neutralizing antibodies to DENV1-4 serotypes were reported in 84% of infants by 9 months. Significantly lower neutralizing antibody titers were also reported in 9-month-old infants compared to that in 6-month-old infants and infants at birth. Comparable levels of enhancement of DENV1-4 infection at a particular dilution to at least one serotype were noted in infants at 3 and 6 months of age. Fold enhancement of DENV1-4 infection was found to be highest in 6-month-old infants at a dilution of 1:20. In summary, our data suggests that DENV infection-enhancing activity aligns with the decline of neutralizing antibodies.

Conclusion: Our study indicates that maternally acquired neutralizing antibodies could be protective until 6 months of age and capable of facilitating ADE on exposure to dengue infections in later months of life.

Keywords: ADE; dengue; infants; infection enhancement; neutralizing antibodies.

Figure 1

(A-D) Age-specific neutralizing antibody titers against each of the four dengue virus serotypes (DENV-1, DENV-2, DENV-3, and DENV-4) in the serum of n=32 infants each at birth i.e., 0, and 3, 6, 9, and 12 months of age. A baseline was drawn for each serotype which is the lower limit of quantitation (LLOQ), indicated by a dotted line (DENV-1 ≥ 16, DENV-2 ≥ 13, DENV-3 ≥ 11, and DENV-4 ≥ 11). P-values were calculated using the Mann–Whitney U-test (*p<0.01, **p<0.001, ***p<0.0001, ****p<0.0001). (E-H) Dengue virus serotype 1-4-specific positive infection enhancement at a particular dilution in serially diluted infant serum samples at different months of age (n=32 each at birth i.e., 0, and 3, 6, 9, and 12 months of age). Fold enhancement was measured as the fold increase in the DENV-infected cells relative to that in DENV-naive control. The dotted line indicates the cut-off value for each serotype above which positive enhancement was seen at different dilutions (DENV-1 ≥ 80, DENV-2 ≥ 20, DENV-3 ≥ 100, and DENV-4 ≥ 60 ffu/ml). P-values were calculated using the Mann–Whitney U-test (*p<0.01, **p<0.001). (I-L) Correlation of enhancing dilution (dilution at which enhancement of infection was observed) and neutralizing titers for all infant samples in a group including all 160 samples. A positive correlation was established by Spearman’s test (r=0.71, p<0.0001 for DENV-1; r=0.73, p<0.0001 for DENV-2; r=0.72, p<0.0001 for DENV-3; and r=0.74, p<0.0001 for DENV-4).

Figure 2

Kinetics of (A-E) DENV-1, (F-J) DENV-2, (K-O) DENV-3, and (P-T) DENV-4 infection enhancement in serially diluted infant serum samples at 0, 3, 6, 9, and 12 months of age (n=32).