Decreased Type I Interferon Production by Plasmacytoid Dendritic Cells Contributes to Severe Dengue
Frontiers in Immunology | December 17, 2020
Upasani V, Scagnolari C, Frasca F, Smith N, Bondet V, Vanderlinden A, Lay S, Auerswald H, Heng S, Laurent D, Ly S, Duong V, Antonelli G, Dussart P, Duffy D and Cantaert T
Frontiers in immunology. 2020;11:605087
Dengue virus is an arthropod-transmitted viral disease of the genus Flavivirus (family Flaviviridae). The virus is endemic in more than 100 countries, and currently half of the world population is at risk of infection (1). An estimate made in 2010 approximates 390 million dengue infections per year, of which 96 million had clinical manifestations (2). DENV strains are distinguished into four antigenically distinct serotypes, DENV-1 to DENV-4, which co-circulate in the same hyperendemic areas (3). Dengue virus infection can cause a spectrum of clinical presentations ranging from asymptomatic infection to more severe forms of disease such as dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS). Pathogenesis of severe dengue is complex and probably results from an exacerbated host immune response. Most primary infections are mild and are likely to provide lifelong protection against the infecting serotype. In contrast, heterotypic secondary DENV infection (with a DENV serotype distinct from the primary infecting serotype) is the greatest risk factor for severe disease (4, 5). Manifestations of severe disease coincide with a drop in viral load and an inflammatory cytokine storm of unknown origin (6).
Type I IFNs (IFN-I), mainly represented by IFNα and -β, are cytokines involved in orchestrating innate and adaptive immune responses against viral infections. However, systemic and excessive productions of IFN-I are known to have detrimental effects to the host, as they correlate with inflammation, immunosuppression and homeostatic dysfunction (7). IFN-I responses are mainly triggered through the binding of viral RNA to RIG-I-like receptors (RLRs), RIG-I, and MDA5, along with endosomal Toll-like receptor 3 (TLR3) and TLR7 (8). IFN regulatory factor (IRF) 3 and 7 are primary transcriptional factors downstream of RLRs/TLRs signaling, and promote IFN-I response induction during DENV infection (9, 10), albeit IRF7 plays a more important role than IRF3 in stimulating the early production of IFN-I (11). In order to balance IFN-I defense with inflammatory damage, FOXO3, a member of the forkhead family of transcription factors, has been recently identified as a negative regulator of IRF7 transcription (12).
DENV evasion strategies interfering with IFN-I production have been identified from in vitro studies. Indeed, DENV overcomes IFN-I-defense mechanisms in primary human immune cells, which appear to have a key role in modulating pathogenesis (13). However, the in vivo direct implications of the IFN-I evasion mechanisms adopted by DENV have, so far, been poorly explored, mainly due to the technical challenges to detect low circulating levels of different IFN-I proteins (14–19). Although almost all nucleated cells can produce IFN-Is in response to viral infection, dendritic cells (DCs), and mainly plasmacytoid DCs (pDC) are a major source of IFN-I (20–22). Myeloid DCs (mDC), on the other hand, have been shown to be the predominant target of DENV infection in the peripheral blood (23–25). DENV infection impairs DC function including IFN-I signalling (26), leading to less efficient priming of DENV-specific adaptive immune responses (24). Frequencies of mDCs and pDCs seem to be reduced in the blood of DENV-infected patients during acute phase of disease, but the correlation with disease severity is less clear (27–29).
Here, we aimed to perform a comprehensive evaluation of type I IFN responses during the earliest phase of disease, within 96h of fever onset in a cohort of Cambodian children. We conducted an integrated analysis of expressed genes related to IFN-I signaling in PBMCs, determination of plasma IFNα/β by ultrasensitive digital ELISA and extensive DC subset phenotyping in patients stratified for infection history and disease severity. We show a robust type I IFN response induced after DENV infection compared to healthy individuals. IFNα and IFNβ protein concentrations correlated to DENV viral load and the presence of circulating pDCs in DENV-infected patients. Increased amount of both IFN-I-related transcripts and increased IFNα/β protein concentrations were detected in patients with mild disease compared to severe dengue patients classified as DHF/DSS. In parallel, we observed a correlation between IFNα protein concentrations and platelet counts, a hallmark of severe infection, indicating that a strong and early type I IFN response is beneficial after DENV infection. Finally, IFN-I responses were inversely correlated to anti-DENV antibody titers.
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