Summary Antibodies protect against homologous Dengue virus (DENV) infection but can precipitate severe dengue by promoting heterotypic virus entry via Fcγ receptors (FcγR). We immortalized memory B cells from individuals after primary or secondary infection and analyzed anti-DENV monoclonal antibodies (mAbs) thus generated. MAbs to envelope (E) protein domain III (DIII) were either serotype specific or cross-reactive and potently neutralized DENV infection. DI/DII- or viral membrane protein prM-reactive mAbs neutralized poorly and showed broad cross-reactivity with the four DENV serotypes. All mAbs enhanced infection at subneutralizing concentrations. Three mAbs targeting distinct epitopes on the four DENV serotypes and engineered to prevent FcγR binding did not enhance infection and neutralized DENV in vitro and in vivo as postexposure therapy in a mouse model of lethal DENV infection. Our findings reveal an unexpected degree of cross-reactivity in human antibodies against DENV and illustrate the potential for an antibody-based therapy to control severe dengue.

Dengue virus (DV) is a mosquito‐borne flavivirus that causes haemorrhagic fever in humans. DV primarily targets immature dendritic cells (DCs) after a bite by an infected mosquito vector. Here, we analysed the interactions between DV and human‐monocyte‐derived DCs at the level of virus entry. We show that the DC‐specific ICAM3‐grabbing non‐integrin (DC‐SIGN) molecule, a cell‐surface, mannose‐specific, C‐type lectin, binds mosquito‐cell‐derived DVs and allows viral replication. Conclusive evidence for the involvement of DC‐SIGN in DV infection was obtained by the inhibition of viral infection by anti‐DC‐SIGN antibodies and by the soluble tetrameric ectodomain of DC‐SIGN. Our data show that DC‐SIGN functions as a DV‐binding lectin by interacting with the DV envelope glycoprotein. Mosquito‐cell‐derived DVs may have differential infectivity for DC‐SIGN‐expressing cells. We suggest that the differential use of DC‐SIGN by viral envelope glycoproteins may account for the immunopathogenesis of DVs.

Dengue virus (DV) is a mosquito-borne flavivirus that causes hemorrhagic fever in humans. In the natural infection, DV is introduced into human skin by an infected mosquito vector where it is believed to target immature dendritic cells (DCs) and Langerhans cells (LCs). We found that DV productively infects DCs but not LCs. We show here that the interactions between DV E protein, the sole mannosylated glycoprotein present on DV particles, and the C-type lectin dendritic cell-specific intercellular adhesion molecule 3-grabbing non-integrin (DC-SIGN) are essential for DV infection of DCs. Binding of mannosylated N-glycans on DV E protein to DC-SIGN triggers a rapid and efficient internalization of the viral glycoprotein. However, we observed that endocytosisdefective DC-SIGN molecules allow efficient DV replication, indicating that DC-SIGN endocytosis is dispensable for the internalization step in DV entry. Together, these results argue in favor of a mechanism by which DC-SIGN enhances DV entry and infection in cis. We propose that DC-SIGN concentrates mosquito-derived DV particles at the cell surface to allow efficient interaction with an as yet unidentified entry factor that is ultimately responsible for DV internalization and pHdependent fusion into DCs.

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BackgroundAn important question in dengue pathogenesis is the identity of immune cells involved in the control of dengue virus infection at the site of the mosquito bite. There is evidence that infection of immature myeloid dendritic cells plays a crucial role in dengue pathogenesis and that the interaction of the viral envelope E glycoprotein with CD209/DC-SIGN is a key element for their productive infection. Dermal macrophages express CD209, yet little is known about their role in dengue virus infection.Methods and FindingsHere, we showed that dermal macrophages bound recombinant envelope E glycoprotein fused to green fluorescent protein. Because dermal macrophages stain for IL-10 in situ, we generated dermal-type macrophages from monocytes in the presence of IL-10 to study their infection by dengue virus. The macrophages were able to internalize the virus, but progeny virus production was undetectable in the infected cells. In addition, no IFN-α was produced in response to the virus. The inability of dengue virus to grow in the macrophages was attributable to accumulation of internalized virus particles into poorly-acidified phagosomes.ConclusionsAborting infection by viral sequestration in early phagosomes would present a novel means to curb infection of enveloped virus and may constitute a prime defense system to prevent dengue virus spread shortly after the bite of the infected mosquito.

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