Therapeutic opportunities in dengue infection

Association of viral kinetics, infection history, NS1 protein with plasma leakage among Indonesian dengue infected patients

OBJECTIVES

Plasma leakage, a hallmark of disease in Dengue virus (DENV) infection, is an important clinical manifestation and is often associated with numerous factors such as viral factors. The aim of this study is to investigate the association of virus serotype, viral load kinetics, history of infection, and NS1 protein with plasma leakage.

METHODS

Subjects with fever ≤ 48 hours and positive DENV infection were included. Serial laboratory tests, viral load measurements, and ultrasonography examination to assess plasma leakage were performed.

RESULTS

DENV-3 was the most common serotype found in the plasma leakage group (35%). Patients with plasma leakage demonstrated a trend of higher viral load and a longer duration of viremia compared to those without. This was significantly observed on the fourth day of fever (p = 0.037). We found higher viral loads on specific days in patients with plasma leakage in both primary and secondary infections compared to those without. In addition, we also observed more rapid viral clearance in patients with secondary infection. NS1 protein, especially after 4 days of fever, was associated with higher peak viral load level, even though it was not statistically significant (p = 0.470). However, pairwise comparison demonstrated that peak viral load level in the group of patients with circulating NS1 detected for 7 days was significantly higher than the 5-day group (p = 0.037).

CONCLUSION

DENV-3 was the most common serotype to cause plasma leakage. Patients with plasma leakage showed a trend of higher viral load and a longer duration of viremia. Higher level of viral load was observed significantly on day 5 in patients with primary infection and more rapid viral clearance was observed in patients with secondary infection. Longer duration of circulating NS1 protein was also seen to be positively correlated with higher peak viral load level although not statistically significant.

Administration of plasmacytoid dendritic cell-stimulative lactic acid bacteria is effective against dengue virus infection in mice

Dengue virus (DENV), a mosquito‑borne flavivirus, causes an acute febrile illness that is a major public health problem in the tropics and subtropics globally. However, methods to prevent or treat DENV infection have not been well established. It was previously demonstrated that Lactococcus lactis strain plasma (LC‑plasma) has the ability to stimulate plasmacytoid dendritic cells (pDCs). As pDCs are key immune cells that control viral infection by producing large amounts of type I interferons (IFN), the present study evaluated the effect of LC‑plasma on DENV infection using a mouse infectious DENV strain. Mice were divided into two groups and the test group was orally administered LC‑plasma for two weeks. Two weeks following administration, the mice were infected with DENV and the relative viral titers and the expression of the inflammatory genes in DENV‑infected tissue were measured using reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR). The relative viral titers were notably lower in the DENV‑infected tissues compared with the control group when LC‑plasma was orally administered prior to DENV infection. Furthermore, the expression of the inflammatory genes associated with DENV infection was also reduced by LC‑plasma administration. To investigate how LC‑plasma administration controls DENV infection, the present study examined anti‑viral gene expression, which is critical for the viral clearance induced by type I IFN. Two weeks subsequent to the administration of LC‑plasma, the expression of anti‑viral gene was measured using RT‑qPCR. Oral intake of LC‑plasma enhanced anti‑viral gene expression in DENV‑infected spleen tissue. To clarify the detailed mechanism, in vitro co‑culture studies using bone‑marrow derived DC (BMDC) were performed. BMDC were stimulated with LC‑plasma in combination with anti‑IFN‑α/β antibody and the expression of anti‑viral genes was measured. In vitro studies revealed that the effect of LC‑plasma on anti‑viral genes was dependent on type I IFN. Based on these results, LC‑plasma may be effective against DENV infection by stimulating pDCs, which results in the increased production of anti‑viral factors.

Dengue virus infection: current concepts in immune mechanisms and lessons from murine models

Dengue viruses (DENV), a group of four serologically distinct but related flaviviruses, are responsible for one of the most important emerging viral diseases. This mosquito-borne disease has a great impact in tropical and subtropical areas of the world in terms of illness, mortality and economic costs, mainly due to the lack of approved vaccine or antiviral drugs. Infections with one of the four serotypes of DENV (DENV-1-4) result in symptoms ranging from an acute, self-limiting febrile illness, dengue fever, to severe dengue haemorrhagic fever or dengue shock syndrome. We reviewed the existing mouse models of infection, including the DENV-2-adapted strain P23085. The role of CC chemokines, interleukin-17 (IL-17), IL-22 and invariant natural killer T cells in mediating the exacerbation of disease in immune-competent mice is highlighted. Investigations in both immune-deficient and immune-competent mouse models of DENV infection may help to identify key host–pathogen factors and devise novel therapies to restrain the systemic and local inflammatory responses associated with severe DENV infection.

Inflammatory and innate immune responses in dengue infection: protection versus disease induction

Dengue disease is a mosquito-borne viral disease of expanding geographical range and incidence. Infection by one of the four serotypes of dengue virus induces a spectrum of disease manifestations, ranging from asymptomatic to life-threatening Dengue hemorrhagic fever/dengue shock syndrome. Many efforts have been made to elucidate several aspects of dengue virus-induced disease, but the pathogenesis of disease is complex and remains unclear. Understanding the mechanisms involved in the early stages of infection is crucial to determine and develop safe therapeutics to prevent the severe outcomes of disease without interfering with control of infection. In this review, we discuss the dual role of the innate and inflammatory pathways activated during dengue disease in mediating both protection and exacerbation of disease. We show that some mediators involved in each of these responses differ substantially, suggesting that interfering in disease-associated immune pathways may represent a potential therapeutic opportunity for the treatment of severe dengue.

A model of DENV-3 infection that recapitulates severe disease and highlights the importance of IFN-γ in host resistance to infection

There are few animal models of dengue infection, especially in immunocompetent mice. Here, we describe alterations found in adult immunocompetent mice inoculated with an adapted Dengue virus (DENV-3) strain. Infection of mice with the adapted DENV-3 caused inoculum-dependent lethality that was preceded by several hematological and biochemical changes and increased virus dissemination, features consistent with severe disease manifestation in humans. IFN-γ expression increased after DENV-3 infection of WT mice and this was preceded by increase in expression of IL-12 and IL-18. In DENV-3-inoculated IFN-γ(-/-) mice, there was enhanced lethality, which was preceded by severe disease manifestation and virus replication. Lack of IFN-γ production was associated with diminished NO-synthase 2 (NOS2) expression and higher susceptibility of NOS2(-/-) mice to DENV-3 infection. Therefore, mechanisms of protection to DENV-3 infection rely on IFN-γ-NOS2-NO-dependent control of viral replication and of disease severity, a pathway showed to be relevant for resistance to DENV infection in other experimental and clinical settings. Thus, the model of DENV-3 infection in immunocompetent mice described here represents a significant advance in animal models of severe dengue disease and may provide an important tool to the elucidation of immunopathogenesis of disease and of protective mechanisms associated with infection.