Differences in type I interferon signaling antagonism by dengue viruses in human and non-human primate cell lines

Are viral loads in the febrile phase a predictive factor of dengue disease severity?

Background

As many studies have shown conflicting results regarding the extent of viraemia and clinical disease severity, we sought to investigate if viraemia during early dengue illness is associated with subsequent clinical disease severity.

Methods

Realtime PCR was carried out to identify the dengue virus (DENV serotype), in 362 patients, presenting within the first 4 days of illness, from 2017 to 2022, in Colombo Sri Lanka. To characterize subsequent clinical disease severity, all patients were followed throughout their illness daily and disease severity classified according to WHO 1997 and 2009 disease classification.

Results

263 patients had DF, 99 progressed to develop DHF, and 15/99 with DHF developed shock (DSS). Although the viral loads were higher in the febrile phase in patients who progressed to develop DHF than in patients with DF this was not significant (p=0.5). Significant differences were observed in viral loads in patients infected with different DENV serotypes (p=0.0009), with lowest viral loads detected in DENV2 and the highest viral loads in DENV3. Sub-analysis for association of viraemia with disease severity for each DENV serotyped was again not significant. Although those infected with DENV2 had lower viral loads, infection with DENV2 was significantly associated with a higher risk of developing DHF (p=0.011, Odds ratio 1.9; 95% CI 1.164 to 3.078). Based on the WHO 2009 disease classification, 233 had dengue with warning signs (DWW), 114 dengue without warning signs (DWoWS), and 15 had severe dengue (SD). No significant difference was observed in the viral loads between those with SD, DWW and DWoWS (p=0.27).

Conclusions

Viral loads were significantly different in the febrile phase between different DENV serotypes, and do not appear to significantly associate with subsequent clinical disease severity in a large Sri Lankan cohort.

The Roles of Type I Interferon in Co-infections With Parasites and Viruses, Bacteria, or Other Parasites

Parasites, bacteria, and viruses pose serious threats to public health. Many parasite infections, including infections of protozoa and helminths, can inhibit inflammatory responses and impact disease outcomes caused by viral, bacterial, or other parasitic infections. Type I interferon (IFN-I) has been recognized as an essential immune effector in the host defense against various pathogens. In addition, IFN-I responses induced by co-infections with different pathogens may vary according to the host genetic background, immune status, and pathogen burden. However, there is only limited information on the roles of IFN-I in co-infections with parasites and viruses, bacteria, or other parasites. This review summarizes some recent findings on the roles of IFN-I in co-infections with parasites, including Leishmania spp., Plasmodium spp., Eimeria maxima, Heligmosomoides polygyrus, Brugia malayi, or Schistosoma mansoni, and viruses or bacteria and co-infections with different parasites (such as co-infection with Neospora caninum and Toxoplasma gondii, and co-infection with Plasmodium spp. and H. polygyrus). The potential mechanisms of host responses associated with co-infections, which may provide targets for immune intervention and therapies of the co-infections, are also discussed.

Duration of the Presence of Infectious Zika Virus in Semen and Serum

Zika virus (ZIKV) has recently caused a large epidemic in the Americas that is associated with birth defects. Although ZIKV is primarily transmitted by Aedes mosquitoes, ZIKV RNA is detectable in blood and semen of infected individuals for weeks or months, during which sexual and other modes of transmission are possible. However, viral RNA is usually detectable longer than infectious virus is present. We determined the frequency of isolation of infectious virus from semen and serum samples prospectively obtained from a cohort of patients in Puerto Rico. We confirmed isolation of infectious virus on the basis of a tissue culture cytopathic effect, an increase in virus genome copy equivalents (GCE), and positive results of immunofluorescence analysis; virus in infected cells was quantitated by flow cytometry. These criteria confirmed the presence of infectious virus in semen specimens from 8 of 97 patients for up to 38 days after initial detection when virus loads are >1.4 × 106 genome copy equivalents/mL. Two serum isolates were obtained from 296 patients. These findings can help guide important prevention guidelines for persons that may potentially be infectious and transmit ZIKV sexually.

Amazonian Phlebovirus (Bunyaviridae) potentiates the infection of Leishmania (Leishmania) amazonensis: Role of the PKR/IFN1/IL-10 axis

BACKGROUND

Leishmania parasites are transmitted to vertebrate hosts by phlebotomine sandflies and, in humans, may cause tegumentary or visceral leishmaniasis. The role of PKR (dsRNA activated kinase) and Toll-like receptor 3 (TLR3) activation in the control of Leishmania infection highlights the importance of the engagement of RNA sensors, which are usually involved in the antiviral cell response, in the fate of parasitism by Leishmania. We tested the hypothesis that Phlebovirus, a subgroup of the Bunyaviridae, transmitted by sandflies, would interfere with Leishmania infection.

METHODOLOGY/PRINCIPAL FINDINGS

We tested two Phlebovirus isolates, Icoaraci and Pacui, from the rodents Nectomys sp. and Oryzomys sp., respectively, both natural sylvatic reservoir of Leishmania (Leishmania) amazonensis from the Amazon region. Phlebovirus coinfection with L. (L.) amazonensis in murine macrophages led to increased intracellular growth of L. (L.) amazonensis. Further studies with Icoaraci coinfection revealed the requirement of the PKR/IFN1 axis on the exacerbation of the parasite infection. L. (L.) amazonensis and Phlebovirus coinfection potentiated PKR activation and synergistically induced the expression of IFNβ and IL-10. Importantly, in vivo coinfection of C57BL/6 mice corroborated the in vitro data. The exacerbation effect of RNA virus on parasite infection may be specific because coinfection with dengue virus (DENV2) exerted the opposite effect on parasite load.

CONCLUSIONS

Altogether, our data suggest that coinfections with specific RNA viruses shared by vectors or reservoirs of Leishmania may enhance and sustain the activation of host cellular RNA sensors, resulting in aggravation of the parasite infection. The present work highlights new perspectives for the investigation of antiviral pathways as important modulators of protozoan infections.

Experimental in vitro and in vivo systems for studying the innate immune response during dengue virus infections

Dengue is the most prevalent arboviral disease in humans and leads to significant morbidity and socioeconomic burden in tropical and subtropical areas. Dengue is caused by infection with any of the four closely related serotypes of dengue virus (DENV1-4) and usually manifests as a mild febrile illness, but may develop into fatal dengue hemorrhagic fever and shock syndrome. There are no specific antiviral therapies against dengue because understanding of DENV biology is limited. A tetravalent chimeric dengue vaccine, Dengvaxia, has finally been licensed for use, but its efficacy was significantly lower against DENV-2 infections and in dengue-naïve individuals. The identification of mechanisms underlying the interactions between DENV and immune responses will help to determine efficient therapeutic and preventive options. It has been well established how the innate immune system responds to DENV infection and how DENV overcomes innate antiviral defenses, however further progress in this field remains hampered by the absence of appropriate experimental dengue models. Herein, we review the available in vitro and in vivo approaches to study the innate immune responses to DENV.

Zika virus induces massive cytoplasmic vacuolization and paraptosis-like death in infected cells

The cytopathic effects of Zika virus (ZIKV) are poorly characterized. Innate immunity controls ZIKV infection and disease in most infected patients through mechanisms that remain to be understood. Here, we studied the morphological cellular changes induced by ZIKV and addressed the role of interferon-induced transmembrane proteins (IFITM), a family of broad-spectrum antiviral factors, during viral replication. We report that ZIKV induces massive vacuolization followed by "implosive" cell death in human epithelial cells, primary skin fibroblasts and astrocytes, a phenomenon which is exacerbated when IFITM3 levels are low. It is reminiscent of paraptosis, a caspase-independent, non-apoptotic form of cell death associated with the formation of large cytoplasmic vacuoles. We further show that ZIKV-induced vacuoles are derived from the endoplasmic reticulum (ER) and dependent on the PI3K/Akt signaling axis. Inhibiting the Sec61 ER translocon in ZIKV-infected cells blocked vacuole formation and viral production. Our results provide mechanistic insight behind the ZIKV-induced cytopathic effect and indicate that IFITM3, by acting as a gatekeeper for incoming virus, restricts virus takeover of the ER and subsequent cell death.

Distinct expression of interferon-induced protein with tetratricopeptide repeats (IFIT) 1/2/3 and other antiviral genes between subsets of dendritic cells induced by dengue virus 2 infection

Dengue virus (DENV) infection is an emerging public health hazard threatening inhabitants of the tropics and sub-tropics. Dendritic cells (DCs) are one of the major targets of DENV and the initiators of the innate immune response against the virus. However, current in vitro research on the DENV-DC interaction is hampered by the low availability of ex vivo DCs and donor variation. In the current study, we attempted to develop a novel in vitro DC model using immature DCs derived from the myeloid leukaemia cell line MUTZ-3 (IMDCs) to investigate the DENV-DC interaction. The IMDCs morphologically and phenotypically resembled human immature monocyte-derived dendritic cells (IMMoDCs). However, the permissiveness of IMDCs to DENV2 was lower than that of IMMoDCs. RT-PCR arrays showed that a group of type I interferon (IFN) -inducible genes, especially IFIT1, IFITM1, and IFI27, were significantly up-regulated in IMMoDCs but not in IMDCs after DENV2 infection. Further investigation revealed that IFIT genes were spontaneously expressed at both transcriptional and protein levels in the naive IMDCs but not in the naive IMMoDCs. It is possible that the poor permissiveness of IMDCs to DENV2 was a result of the high basal levels of IFIT proteins. We conclude that the IMDC model, although less permissive to DENV2, is a useful platform for studying the suppression mechanism of DENV2 and we expand the knowledge of cellular factors that modulate DENV2 infection in the human body.

The role of the unfolded protein response in dengue virus pathogenesis

Symptomatic dengue virus (DENV) infections range from mild fever to severe haemorrhagic disease and death. Host-viral interactions play a significant role in deciding the fate of the infection. The unfolded protein response (UPR) is a prosurvival cellular reaction induced in response to DENV-mediated endoplasmic reticulum stress. The UPR has complex interactions with the cellular autophagy machinery, apoptosis, and innate immunity. DENV has evolved to manipulate the UPR to facilitate its replication and to evade host immunity. Our knowledge of this intertwined network of events is continuously developing. A better understanding of the UPR mediated antiviral and proviral effects will shed light on dengue disease pathogenesis and may help development of anti-DENV therapeutics. This review summarizes the role of the UPR in viral replication, autophagy, and DENV-induced inflammation to describe how a host response contributes to DENV pathogenesis.

Drivers of Inter-individual Variation in Dengue Viral Load Dynamics

Dengue is a vector-borne viral disease of humans that endemically circulates in many tropical and subtropical regions worldwide. Infection with dengue can result in a range of disease outcomes. A considerable amount of research has sought to improve our understanding of this variation in disease outcomes and to identify predictors of severe disease. Contributing to this research, patterns of viral load in dengue infected patients have been quantified, with analyses indicating that peak viral load levels, rates of viral load decline, and time to peak viremia are useful predictors of severe disease. Here, we take a complementary approach to understanding patterns of clinical manifestation and inter-individual variation in viral load dynamics. Specifically, we statistically fit mathematical within-host models of dengue to individual-level viral load data to test virological and immunological hypotheses explaining inter-individual variation in dengue viral load. We choose between alternative models using model selection criteria to determine which hypotheses are best supported by the data. We first show that the cellular immune response plays an important role in regulating viral load in secondary dengue infections. We then provide statistical support for the process of antibody-dependent enhancement (but not original antigenic sin) in the development of severe disease in secondary dengue infections. Finally, we show statistical support for serotype-specific differences in viral infectivity rates, with infectivity rates of dengue serotypes 2 and 3 exceeding those of serotype 1. These results contribute to our understanding of dengue viral load patterns and their relationship to the development of severe dengue disease. They further have implications for understanding how dengue transmissibility may depend on the immune status of infected individuals and the identity of the infecting serotype.

Dengue is an important vector-borne disease that infects four-hundred million individuals annually. Infection results in a wide range of clinical symptoms. Though many risk factors of dengue are known, the mechanisms explaining why an individual will suffer severe symptoms are poorly understood. Clinical studies have shown characteristics of viral load kinetics of dengue-infected individuals may be indicators of disease severity. However, viral load measurements vary considerably by individual. Here we use statistical methods to empirically test hypotheses that may explain variation in dengue viral load patterns by clinical manifestation and by serotype. We show that there is statistical support for antibodies being responsible for higher disease severity during secondary dengue infections and for high viral infectivity rates of dengue serotypes 2 and 3 relative to dengue 1. These results further understanding of the relationship between viral load patterns and severe dengue disease and have important implications for dengue transmissibility.