Given the ability of D29 Fab-IgG to bind both prM and E on western blots, immunoprecipitation was carried out with DENV2infected BHK cell lysate to elucidate if D29 Fab-IgG binds both proteins in solution. An initial radioactive immunoprecipitation showed D29 Fab-IgG binding to both E (,55 kDa) and prM (,20 kDa), as both proteins are precipitated whereas h4G2 only precipitated E protein (Fig. 3A) . However, as prM intrinsically interacts with E to form heterodimers, it is possible that antibody binding to one of the components in the heterodimer would pull down the other. To address this, dissociation of the heterodimer with 1.25% SDS was performed prior to the assay. Immunoprecipitated proteins were resolved by reducing SDS-PAGE and visualized by silver staining. Identity of the precipitated proteins was verified by non-reducing Western blot analysis with h3H5 and m2H2, respectively (Fig. 3B ). The control antibodies were able to precipitate their corresponding binding partners. Despite the ability to recognize both prM and E on western blots, D29 Fab-IgG only precipitated prM. Taken collectively, our data indicate that D29 binds both prM and E but the epitope on E is not accessible on the native protein.