Dengue virus infects the mouse eye following systemic or intracranial infection and induces inflammatory responses

The Dynamic Relationship between Dengue Virus and the Human Cutaneous Innate Immune Response

Dengue virus (DENV) is a continuing global threat that puts half of the world's population at risk for infection. This mosquito-transmitted virus is endemic in over 100 countries. When a mosquito takes a bloodmeal, virus is deposited into the epidermal and dermal layers of human skin, infecting a variety of permissive cells, including keratinocytes, Langerhans cells, macrophages, dermal dendritic cells, fibroblasts, and mast cells. In response to infection, the skin deploys an array of defense mechanisms to inhibit viral replication and prevent dissemination. Antimicrobial peptides, pattern recognition receptors, and cytokines induce a signaling cascade to increase transcription and translation of pro-inflammatory and antiviral genes. Paradoxically, this inflammatory environment recruits skin-resident mononuclear cells that become infected and migrate out of the skin, spreading virus throughout the host. The details of the viral-host interactions in the cutaneous microenvironment remain unclear, partly due to the limited body of research focusing on DENV in human skin. This review will summarize the functional role of human skin, the cutaneous innate immune response to DENV, the contribution of the arthropod vector, and the models used to study DENV interactions in the cutaneous environment.

Ocular Autoimmune Systemic Inflammatory Infectious Study (OASIS) - Report 6: Dengue Uveitis at a Tertiary Eye Institution in Singapore

OBJECTIVES

To identify the characteristics, treatment, and visual outcomes of dengue uveitis at a tertiary eye care centre in Singapore.

METHODS

Retrospective case record review of all consecutive dengue uveitis patients (2004 to 2015) from the Ocular Autoimmune Systemic Inflammatory and Infectious Study (OASIS) database.

RESULTS

Fifty-four patients were identified from the OASIS database. The most common ocular symptom was blurring of vision (n = 41, 75.9%), followed by floaters (n = 9, 17.0%), scotoma (n = 5, 9.3%), and metamorphopsia (n = 3, 5.7%). Scotoma based on history, Amsler grid, and perimetry accounted for 27 (50%) patients. Majority presented with either a posterior uveitis or retinal vasculitis (n = 51, 94.4%). Treatments ranged from close observation for spontaneous improvement, to the use of high-dose corticosteroids.

CONCLUSIONS

Dengue uveitis may present with a spectrum of disease manifestations including posterior uveitis, vasculitis, and macula edema. Scotoma is significant and may be found on history taking, Amsler charting, and perimetry.

Dengue Virus Infection of Human Retinal Müller Glial Cells

Retinopathy is a recently recognized complication of dengue, affecting up to 10% of hospitalized patients. Research on the pathogenesis has focused largely on effects of dengue virus (DENV) at the blood-retinal barrier. Involvement of retinal Müller glial cells has received little attention, although this cell population contributes to the pathology of other intraocular infections. The goal of our work was to establish the susceptibility of Müller cells to infection with DENV and to identify characteristics of the cellular antiviral, inflammatory, and immunomodulatory responses to DENV infection in vitro. Primary human Müller cell isolates and the MIO-M1 human Müller cell line were infected with the laboratory-adapted Mon601 strain and DENV serotype 1 and 2 field isolates, and cell-DENV interactions were investigated by immunolabelling and quantitative real-time polymerase chain reaction. Müller cells were susceptible to DENV infection, but experiments involving primary cell isolates indicated inter-individual variation. Viral infection induced an inflammatory response (including tumour necrosis factor-α, interleukin [IL]-1β, and IL-6) and an immunomodulatory response (including programmed death-ligand [PD-L]1 and PD-L2). The type I interferon response was muted in the Müller cell line compared to primary cell isolates. The highest infectivity and cell responses were observed in the laboratory-adapted strain, and overall, infectivity and cell responses were stronger in DENV2 strains. This work demonstrates that Müller cells mount an antiviral and immune response to DENV infection, and that this response varies across cell isolates and DENV strain. The research provides a direction for future efforts to understand the role of human retinal Müller glial cells in dengue retinopathy.

Zika virus infection of retinal cells and the developing mouse eye induces host responses that contrasts to the brain and dengue virus infection

Zika virus (ZIKV) infection causes ocular and neurological pathologies with ZIKV-induction of developmental abnormalities following in utero infection a major concern. The study here has compared ZIKV and the related dengue virus (DENV) infection in the eye and brain. In vitro, both ZIKV and DENV could infect cell lines representing the retinal pigmented epithelium, endothelial cells, and Mueller cells, with distinct innate responses in each cell type. In a 1-day old mouse challenge model, both ZIKV and DENV infected the brain and eye by day 6 post-infection (pi). ZIKV was present at comparable levels in both tissues, with RNA increasing with time post-infection. DENV infected the brain, but RNA was detected in the eye of less than half of the mice challenged. NanoString analysis demonstrated comparable host responses in the brain for both viruses, including induction of mRNA for myosin light chain-2 (Mly2), and numerous antiviral and inflammatory genes. Notably, mRNA for multiple complement proteins were induced, but C2 and C4a were uniquely induced by ZIKV but not DENV. Consistent with the viral infection in the eye, DENV induced few responses while ZIKV induced substantial inflammatory and antiviral responses. Compared to the brain, ZIKV in the eye did not induce mRNAs such as C3, downregulated Retnla, and upregulated CSF-1. Morphologically, the ZIKV-infected retina demonstrated reduced formation of specific retinal layers. Thus, although ZIKV and DENV can both infect the eye and brain, there are distinct differences in host cell and tissue inflammatory responses that may be relevant to ZIKV replication and disease.

Viperin is anti-viral in vitro but is dispensable for restricting dengue virus replication or induction of innate and inflammatory responses in vivo

Viperin has antiviral function against many viruses, including dengue virus (DENV), when studied in cells in culture. Here, the antiviral actions of viperin were defined both in vitro and in a mouse in vivo model of DENV infection. Murine embryonic fibroblasts (MEFs) derived from mice lacking viperin (vip^−/−) showed enhanced DENV infection, accompanied by increased IFN-β and induction of ISGs; IFIT1 and CXCL-10 but not IRF7, when compared to wild-type (WT) MEFs. In contrast, subcutaneous challenge of immunocompetent WT and vip^−/− mice with DENV did not result in enhanced infection. Intracranial infection with DENV resulted in body weight loss and neurological disease with a moderate increase in mortality in vip^−/− compared with WT mice, although this was not accompanied by altered brain morphology, immune cell infiltration or DENV RNA level in the brain. Similarly, DENV induction of IFN-β, IFIT1, CXCL-10, IRF7 and TNF-α was not significantly different in WT and vip^−/− mouse brain, although there was a modest but significant increase in DENV induction of IL-6 and IfI27la in the absence of viperin. NanoString nCounter analysis confirmed no significant difference in induction of a panel of inflammatory genes in WT compared to vip^−/− DENV-infected mouse brains. Further, polyI:C stimulation of bone marrow-derived macrophages (BMDMs) induced TNF-α, IFN-β, IL-6 and Nos-2, but responses were not different in BMDMs generated from WT or vip^−/− mice. Thus, while there is significant evidence of anti-DENV actions of viperin in some cell types in vitro, for DENV infection in vivo a lack of viperin does not affect systemic or brain susceptibility to DENV or induction of innate and inflammatory responses.