Development of a novel plate reader-based antibody-dependent enhancement (ADE) assay for orthoflavivirus infections

Antibody-dependent enhancement (ADE) is one of the mechanisms associated with severe clinical outcomes in infections caused by certain viruses, including dengue virus (DENV). Several ADE assay systems have been established, including flow cytometric assays using live viruses, enzyme-linked immuno-sorbent assay (ELISA) for the detection of viral NS1, and luciferase reporter gene assays. Among these, the flow cytometric assay is the most commonly used to evaluate ADE activity; however, it has limitations such as high operational costs due to fixation and immunostaining procedures, as well as a long analysis time. Fluorescent protein-expressing single-round infectious particles (SRIPs) enables label-free detection of ADE activity, but the flow cytometric procedure still requires a long analysis time. In this study, to simplify and expedite the ADE assay using enhanced green fluorescent protein (EGFP)-expressing SRIPs, we developed a plate reader-based ADE assay as an alternative to the conventional flow cytometry-based method. To evaluate effectiveness of this assay, we measured ADE activities in K562 cells induced by pan-orthoflavivirus 4G2 and pan-dengue 4E11 monoclonal antibodies (mAbs) using both flow cytometric assays using live viruses and plate-reader-based EGFP-expressing SRIPs assays. The results showed strong correlations between the two different ADE assays with R² values of 0.92 for 4G2 mAb and 0.94 for 4E11 mAb (Pearson correlation coefficients). In summary, this newly established assay offers a high-throughput and cost-effective method for comprehensive characterization of the relationship between vaccine- or infection-induced antibodies and ADE in orthoflavivirus infections.