Travelling with Dengue: From the Skin to the Nodes

Dengue virus (DENV) infects humans through the skin. The early infection and encounters between DENV and cutaneous immune and non‐immune cells only recently are under investigation. We have reported DENV‐infected cutaneous dendritic cells (DCs), also keratinocytes and dermal fibroblasts permissive to DENV infection. Now, upon cutaneously inoculating fluorescently labeled DENV into immune‐competent mice, we found DENV mostly in dermis from 1 h post‐inoculation. Afterwards, DENV rapidly localized in the subcapsular sinus of draining lymph nodes (DLNs) associated with CD169+ macrophages, suggesting virus travelling through lymph flow. However, DENV association with CD11c+ DCs in the paracortex and T:B border suggests DENV being ferried from the skin to DLNs by DCs too. DENV was not associated with F4/80+ macrophages nor with DEC205+ DCs, but it was inside B cell follicles early after cutaneous inoculation. DENV inside B follicles likely affects the development of humoral responses. Antibody responses deserve very careful scrutiny as neutralizing memory antibodies are crucial to counteract homotypic reinfections whereas non‐neutralizing ones might facilitate heterotypic DENV infection or even Zika infection, another flavivirus. Unravelling the DENV journey from skin to lymph into regional nodes and the cellular compartments will aid to understand the disease, its pathology and how to counteract it

Dengue Virus Type 2: Protein Binding and Active Replication in Human Central Nervous System Cells

An increased number of dengue cases with neurological complications have been reported in recent years. The lack of reliable animal models for dengue has hindered studies on dengue virus (DENV) pathogenesis and cellular tropism in vivo. We further investigate the tropism of DENV for the human central nervous system (CNS), characterizing DENV interactions with cell surface proteins in human CNS cells by virus overlay protein binding assays (VOPBA) and coimmunoprecipitations. In VOPBA, three membrane proteins (60, 70, and 130 kDa) from the gray matter bound the entire virus particle, whereas only a 70 kDa protein bound in white matter. The coimmunoprecipitation assays revealed three proteins from gray matter consistently binding virus particles, one clearly distinguishable protein (~32 kDa) and two less apparent proteins (100 and 130 kDa). Monoclonal anti-NS3 targeted the virus protein in primary cell cultures of human CNS treated with DENV-2, which also stained positive for NeuH, a neuron-specific marker. Thus, our results indicate (1) that DENV-2 exhibited a direct tropism for human neurons and (2) that human neurons sustain an active DENV replication as was demonstrated by the presence of the NS3 viral antigen in primary cultures of these cells treated with DENV-2

Activation of the Innate Immune Response against DENV in Normal Non-Transformed Human Fibroblasts

In this work, we demonstrate that that both human whole skin and freshly isolated skin fibroblasts are productively infected with Dengue virus (DENV). In addition, primary skin fibroblast cultures were established and subsequently infected with DENV-2; we showed in these cells the presence of the viral antigen NS3, and we found productive viral infection by a conventional plaque assay. Of note, the infectivity rate was almost the same in all the primary cultures analyzed from different donors. The skin fibroblasts infected with DENV-2 underwent signaling through both TLR3 and RIG-1, but not Mda5, triggering up-regulation of IFNβ, TNFα, defensin 5 (HB5) and β defensin 2 (HβD2). In addition, DENV infected fibroblasts showed increased nuclear translocation of interferon (IFN) regulatory factor 3 (IRF3), but not interferon regulatory factor 7 IRF7, when compared with mock-infected fibroblasts. Our data suggest that fibroblasts might even participate producing mediators involved in innate immunity that activate and contribute to the orchestration of the local innate responses. This work is the first evaluating primary skin fibroblast cultures obtained from different humans, assessing both their susceptibility to DENV infection as well as their ability to produce molecules crucial for innate immunity

dsRNA weakly colocalizes with lipid raft markers in DENV-infected HMEC-1.

<p>(A) HMEC-1 cells, mock infected or infected with DENV-2, were fixed 48 h after infection, permeabilized, and analyzed by immunofluorescence. Cells were double stained with mouse monoclonal antibodies against dsRNA (red always) and NS2B (green) (a); dsRNA and NS3 (green) (b); dsRNA and NS5 (green) (c);(B) dsRNA and Cav-1 (green) (a); or dsRNA and flotillin (green) (b). Colocalization of dsRNA was observed at different times after infection. (C)HMEC-1cells were infected with DENV-2 and double stained at different times after infection (18 h and 24 h) dsRNA, red, Cav-1, green; and mock infected, not shown. Nuclear DNA was counterstained with DAPI, and the merged image is shown at higher magnification.</p

Expression and purification of domain III proteins from Dengue and Zika viruses

The envelope (E) protein from Dengue and Zika viruses comprises three functional and structural domains (DI, DII, and DIII). Domain III induces most of the neutralizing antibodies and, as such, is considered as having the highest antigenic potential for the evaluation of population-level surveillance and for detecting past infections in both Dengue and Zika patients. The present study aimed to clone and express recombinant proteins of domain III from Dengue virus serotype 2 and from Zika virus in a prokaryotic system, as well as evaluate their immunogenicity and cross-reactivity. Both antigens were successfully purified and their antigenicity was assessed in mice. The antibodies elicited by domain III of Zika and Dengue virus antigens recognized specifically the native proteins in infected cells. Furthermore, the antigens showed a more specific immunogenic response than that of domain III proteins from Dengue virus. The generated recombinant proteins can be potentially used in subunit vaccines or for surveillance studies

DENV-2 NS3 with Cav-1 colocalize at early stages after infection.

<p>(A) HMEC-1cells were infected with DENV-2 and double stained at different times after infection (12, 24 and 48hpi) or were mock infected (not shown). In all cases, cells were double stained with mouse monoclonal antibodies against NS3 (green) and the lipid raft marker Cav-1 (red). Nuclear DNA was stained with DAPI. (B) Slides were analyzed by confocal laser scanning microscopy (Leica SP5 Objective HCXPLAPO63 63Oil). The graph shows the colocalization index. (C) HMEC-1 cells were transfected with (a) NS2BNS3pro-GFP, (b) NS3pro-GFP, and,(c) NS2B-GFP. After 24 h, they were stained with the lipid raft marker Cav-1 (red), and colocalization was analyzed.</p

Depletion of cholesterol by MβCD affects DENV-2 infection in HMEC-1.

<p>HMEC-1cells were infected at 10 MOI. At 120 min after adsorption, the inoculated virus was washed off, and the cells were cultured in fresh medium. At 2 or 6 h post infection, the cells were mock treated (A) or treated with 10 mM MβCD (B) for 2 h. The drug was then washed off, and the cells were cultured in fresh serum-free medium for 48 h. Detergent-resistant membrane fractions obtained from sucrose gradient ultracentrifugation were collected, and Cav-1 and NS3 were analyzed. The recovered fractions were numbered from 1 (top fraction) to 11 (bottom fraction). (C) The culture supernatants were harvested to determine the viral titration by plaque-forming assays. (D) Disaggregation of lipid rafts after10 mM MβCD treatment.</p

Colocalizationanalysis of DENV NS2B, NS3, and NS5 with caveolin and flotillin in infected cells.

<p>HMEC-1 cells were mock infected or infected with DENV-2, fixed 36 h after infection with 4% paraformaldehyde, permeabilized, and immunolabeled. Cells were double stained with mouse monoclonal antibodies against NS2B (A), NS3 (B), or NS5 (C); the lipid raft markers Cav-1 (upper panel) and Flt-1 (middle panel); and the non-raft marker TfR (bottom panel). DAPI was used for nuclear DNA staining. Slides were analyzed by confocal laser scanning microscopy. (D) The degree of overlap between the green and red signals for each viral protein was statistically analyzed and expressed as a Pearson's coefficient by the microscopy software.</p