Sensing of Immature Particles Produced by Dengue Virus Infected Cells Induces an Antiviral Response by Plasmacytoid Dendritic Cells

Abstract

Dengue virus (DENV) is the leading cause of mosquito-borne viral illness and death in humans. Like many viruses, DENV has evolved potent mechanisms that abolish the antiviral response within infected cells. Nevertheless, several in vivo studies have demonstrated a key role of the innate immune response in controlling DENV infection and disease progression. Here, we report that sensing of DENV infected cells by plasmacytoid dendritic cells (pDCs) triggers a robust TLR7-dependent production of IFNα, concomitant with additional antiviral responses, including inflammatory cytokine secretion and pDC maturation. We demonstrate that unlike the efficient cell-free transmission of viral infectivity, pDC activation depends on cell-to-cell contact, a feature observed for various cell types and primary cells infected by DENV, as well as West Nile virus, another member of the Flavivirus genus. We show that the sensing of DENV infected cells by pDCs requires viral envelope protein-dependent secretion and transmission of viral RNA. Consistently with the cell-to-cell sensing-dependent pDC activation, we found that DENV structural components are clustered at the interface between pDCs and infected cells. The actin cytoskeleton is pivotal for both this clustering at the contacts and pDC activation, suggesting that this structural network likely contributes to the transmission of viral components to the pDCs. Due to an evolutionarily conserved suboptimal cleavage of the precursor membrane protein (prM), DENV infected cells release uncleaved prM containing-immature particles, which are deficient for membrane fusion function. We demonstrate that cells releasing immature particles trigger pDC IFN response more potently than cells producing fusion-competent mature virus. Altogether, our results imply that immature particles, as a carrier to endolysosome-localized TLR7 sensor, may contribute to regulate the progression of dengue disease by eliciting a strong innate response.

Molecular dissection of plasmacytoid dendritic cell activation in vivo during a viral infection

“…First, in vitro , interactions between pDC themselves promote their activation in response to CpG stimulation (Kim et al , ; Saitoh et al , ). Second, co‐culture with infected cells boosts pDC antiviral responses as compared with exposure to free virus, mainly in a cell contact‐dependent manner (Megjugorac et al , ; Takahashi et al , ; Dreux et al , ; Decembre et al , ; Frenz et al , ; Wieland et al , ; Garcia‐Nicolas et al , ). Third, pDC IFN‐I production during MCMV infection requires completion of at least one cycle of viral replication and is more strongly dependent on in vivo viral replication than on the initial viral inoculum dose, suggesting that pDC recognize MCMV‐infected cells rather than viral particles (Robbins et al , ).…”

Cell-Cell Sensing of Viral Infection by Plasmacytoid Dendritic Cells

“…1). In this viral model, the actin network may act as a structural platform for the concentration of PAMP carriers at the contact and thereby for their efficient transmission to the pDCs, leading to TLR7-mediated activation of the IFN response (10). One might speculate that polarization of cellular components at the contacts is a primary feature of the pDC functionality to ensure an efficient antiviral response.…”

“…Especially, DENV-infected cells release vast amounts of noninfectious particles, called immature particles, that can bind to the cell surface but are not competent for membrane fusion. Importantly, DENVinfected cells impaired in the production of immature particles are poor inducers of the pDC response, suggesting that immature particles are the carriers of PAMPs to pDCs (10). Since PAMP recognition by TLR7 is known to occur in the endolysosome compartment, it is tempting to speculate that the immature virions (i.e., those incompetent for membrane fusion) are likely retained in this TLR7-containing endolysosome compartment, resulting in a potent TLR7-mediated IFN response by the pDCs, as opposed to mature particles, which likely escape TLR7 recognition by membrane fusion (10) (Fig.…”

Vaginal Exposure to Zika Virus during Pregnancy Leads to Fetal Brain Infection

“…The genome of flaviviruses (of which ZIKV is a member) is composed of positive-sense RNA. In plasmacytoid dendritic cells (pDCs), a specialized sensor of viruses that secrete large amounts of type I IFNs, Toll-like receptor 7 (TLR7), an endosomal sensor of ssRNA, recognizes the genomic RNA of the incoming virions and mounts antiviral responses to flaviviruses (Bruni et al, 2015; Décembre et al, 2014; Nazmi et al, 2014; Town et al, 2009; Wang et al, 2006; Welte et al, 2009). In contrast, the infected cells sense RNA virus infections by RIG-I (which recognizes 50triphosphorylated dsRNA) and/or MDA5 (which recognizes long dsRNA), which are collectively known as the RIG-I-like receptors (RLRs).…”