Antibody-dependent enhancement representing in vitro infective progeny virus titer correlates with the viremia level in dengue patients
Dengue virus (DENV) distributes throughout tropical and subtropical countries and causes dengue fever (DF) and dengue hemorrhagic fever in humans. Some DF patients suddenly develop severe symptoms after the defervescent period. Although the pathogenic mechanism of the severe symptoms has not been fully elucidated, the viremia level in the early phase has been shown to correlate with the disease severity. One of the hypotheses is that a phenomenon called antibody-dependent enhancement (ADE) of infection leads to a high level of viremia. To examine the plausibility of this hypothesis, we examined the relationship between in vitro ADE activity and in vivo viral load quantity in six patients with dengue diseases. An autologous DENV strain was isolated from each of the six patients. Blood samples were then collected at multiple time points between the acute and defervescent phases, and the balance between neutralizing and enhancing activities against the autologous and prototype viruses was examined. As the antibody levels against DENV were rapidly increased, ADE activity was decreased over time or partially maintained against some viruses at low serum dilution. In addition, positive correlations were observed between ADE activity representing in vitro progeny virus production and viremia levels in patient plasma samples. Therefore, the measurement of ADE activity in dengue-seropositive samples may help to predict the impact of viral load in the subsequent DENV infection. IMPORTANCEIt has not been fully elucidated how the phenomenon of antibody-dependent enhancement (ADE) affects the pathogenesis of severe dengue diseases, although high viremia levels have been epidemiologically demonstrated to be associated with the disease severity. Here, we show that ADE in the acute-phase patient sera exhibited significantly different activities against autologous and lab strains than ADE in the defervescent-phase sera. Further, the enhancement of progeny virus production activity, which is one of the factors to evaluate ADE in vitro, was significantly correlated with the levels of viral load in the patient blood circulation. This suggests that measurement of the in vitro enhancing progeny virus titers might be used to predict the impact of in vivo DENV viremia level. Our present findings could contribute to a method to forecast disease severity for seropositive populations who would be at risk of developing severe disease in the event of heterotypic DENV infection.