Dengue virus infection-enhancing and neutralizing antibody balance in children of the Philippines and Indonesia.

Dengue fever and dengue hemorrhagic fever are important diseases worldwide. Although antibody-dependent enhancement of infection has been proposed as a mechanism for increased disease severity, enhancing antibodies in endemic people have not been thoroughly investigated. Recently, we established a serological assay system to measure the balance of enhancing and neutralizing activities, which provides useful information for estimating in vivo antibody status. We measured the balance of these activities against four dengue virus (DENV) types in endemic populations, and analyzed the proportion of sera containing enhancing and neutralizing antibodies. Predominantly healthy Filipino children were used for analysis, although a population of Indonesian children was also investigated. In the Filipino population, the highest proportion of neutralizing activities was shown against DENV2, followed by DENV1. A greater proportion of sera exhibited enhancing rather than neutralizing antibodies against other virus types. Neutralizing activities were complement-dependent, while enhancing activities were complement-independent. The Indonesian population showed a similar dengue antibody status. Our results indicate that a relatively high proportion of endemic children possessed complement-independent enhancing antibodies against some DENV types.

A simple assay system for infection-enhancing and -neutralizing antibodies to dengue type 2 virus using layers of semi-adherent K562 cells.

A simple alternative to the dengue antibody-dependent enhancement (ADE) assay was established. The new assay method utilizes cells attached to microplate wells, thereby eliminating cumbersome procedures typical of the conventional ADE assay that utilizes suspension cells. Semi-adherent K562 cells bearing the Fc-gamma receptor (Fc gammaR) were cultured on poly-L-lysine-coated plates. The procedure consisted of (i) preparation of a virus-antibody-cell mixture in wells, (ii) cultivation at 37 degrees C for 24 h and (iii) fixation and immunostaining to count infected cells. Using monoclonal antibodies against dengue type 2 virus, the new system correlated with three conventional systems. Additionally, K562 cells were employed in a neutralization test. For this purpose, the virus-antibody mixture was incubated at 37 degrees C for 2 h prior to the addition of cells. As expected, K562 cells provided lower neutralizing antibody titers than did a conventional neutralization test using Vero cells, which do not have Fc gammaR, in monoclonals showing both neutralizing and enhancing activities. Since antibodies are present in polyclonal form in circulation, neutralization tests using K562 cells are considered to reveal a more accurate in vivo status than those using Vero cells. Human sera, positive for dengue virus antibodies, showed neutralizing and enhancing activities in a dose-dependent manner.