A dendritic cell-based assay for measuring memory T cells specific to dengue envelope proteins in human peripheral blood

Highlights for Dengue Immunopathogenesis: Antibody-Dependent Enhancement, Cytokine Storm, and Beyond

Infection with dengue virus (DENV) can lead to a wide spectrum of clinical presentations, ranging from asymptomatic infection to death. It is estimated that the disease manifests only in 90 million cases out of the total 390 million yearly infections. Even though research has not yet elucidated which are the precise pathophysiological mechanisms that trigger severe forms of dengue, the infection elicits a critical immune response significant for dengue pathogenesis development. Understanding how the immune response to DENV is established and how it can resolve the infection or turn into an immunopathology is of great importance in DENV research. Currently, studies have extensively debated 2 hypotheses involving immune response: antibody-dependent enhancement and cytokine storm. However, despite its undeniable importance in severe forms of the disease, these 2 hypotheses are based on a primed immune status resulting from previous heterologous infection, abstaining them from explaining the severe forms of dengue in naive immune subjects, for example. Thus, it seems that a more intricate arrangement of causes and conditions must be achieved to severe dengue to occur. Among them, the cytokine network signature elicited, in association with viral aspects deserves special attention regarding the establishment of infection and evolution to pathogenesis. In this work, we intend to shed light on how those elements contribute to severe dengue development.

Dendritic Cell-Based ELISpot Assay for Assessing T-Cell IFN-γ Responses in Human Peripheral Blood Mononuclear Cells to Dengue Envelope Proteins

Dengue envelope (E) protein is a dominant antigen for vaccine development and E-based vaccines have shown partial or full protection against live-virus challenge in non-human primates. Generally, T cell responses can be investigated with peptides. However, hundreds of over-lapping peptides need to be synthesized to cover the whole sequence of a protein, which brings the cost up to a much higher level than purchasing a protein. We have developed an enzyme-linked immunospot (ELISpot) assay that uses intact E proteins instead of peptides for assessing IFN-gamma (IFN-γ) responses. The assay relies on professional antigen presenting cells, dendritic cells, to process and present the E proteins to stimulate T cells.Peripheral blood mononuclear cells (PBMCs) from dengue-exposed and naïve subjects were selected for the assay development. IFN-γ production ranged from 53 to 513 spot forming units (SFUs) and 0-45 SFUs per million PBMCs in dengue-exposed and naive subject groups, respectively. The assay allowed quantification of E-specific IFN-γ secreting memory T cells in subjects 9 years after exposure to a live-attenuated virus vaccine and live-virus challenge. Our results suggest that the dendritic cell-based IFN-γ assay is a useful tool for assessing immunological memory for clinical research.

How Can Elispot Add Information to Improve Knowledge on Tropical Diseases?

Elispot has been used as an important tool for detecting immune cells' products and functions and has facilitated the understanding of host-pathogen interaction. Despite the incredible diversity of possibilities, two main approaches have been developed: the immunopathogenesis and diagnosis/prognosis of infectious diseases as well as cancer research. Much has been described on the topics of allergy, autoimmune diseases, and HIV-Aids, however, Elispot can also be applied to other infectious diseases, mainly leishmaniasis, malaria, some viruses, helminths and mycosis usually classified as tropical diseases. The comprehension of the function, concentration and diversity of the immune response in the infectious disease is pointed out as crucial to the development of infection or disease in humans and animals. In this review we will describe the knowledge already obtained using Elispot as a method for accessing the profile of immune response as well as the recent advances in information about host-pathogen interaction in order to better understand the clinical outcome of a group of tropical and neglected diseases.

Influenza and dengue virus co-infection impairs monocyte recruitment to the lung, increases dengue virus titers, and exacerbates pneumonia

Co-infections of influenza virus and bacteria are known to cause severe disease, but little information exists on co-infections with other acute viruses. Seasonal influenza and dengue viruses (DENV) regularly co-circulate in tropical regions. The pandemic spread of influenza virus H1N1 (hereafter H1N1) in 2009 led to additional severe disease cases that were co-infected with DENV. Here, we investigated the impact of co-infection on immune responses and pathogenesis in a new mouse model. Co-infection of otherwise sublethal doses of a Nicaraguan clinical H1N1 isolate and two days later with a virulent DENV2 strain increased systemic DENV titers and caused 90% lethality. Lungs of co-infected mice carried both viruses, developed severe pneumonia, and expressed a unique pattern of host mRNAs, resembling only partial responses against infection with either virus alone. A large number of monocytes were recruited to DENV-infected but not to co-infected lungs, and depletion and adoptive transfer experiments revealed a beneficial role of monocytes. Our study shows that co-infection with influenza and DENV impairs host responses, which fail to control DENV titers and instead, induce severe lung damage. Further, our findings identify key inflammatory pathways and monocyte function as targets for future therapies that may limit immunopathology in co-infected patients.

Analysis of cell-mediated immune responses in support of dengue vaccine development efforts

Dengue vaccine development has made significant strides, but a better understanding of how vaccine-induced immune responses correlate with vaccine efficacy can greatly accelerate development, testing, and deployment as well as ameliorate potential risks and safety concerns. Advances in basic immunology knowledge and techniques have already improved our understanding of cell-mediated immunity of natural dengue virus infection and vaccination. We conclude that the evidence base is adequate to argue for inclusion of assessments of cell-mediated immunity as part of clinical trials of dengue vaccines, although further research to identify useful correlates of protective immunity is needed.

Dendritic cells in dengue virus infection: targets of virus replication and mediators of immunity

Dendritic cells (DCs) are sentinels of the immune system and detect pathogens at sites of entry, such as the skin. In addition to the ability of DCs to control infections directly via their innate immune functions, DCs help to prime adaptive B- and T-cell responses by processing and presenting antigen in lymphoid tissues. Infected Aedes aegypti or Aedes albopictus mosquitoes transmit the four dengue virus (DENV) serotypes to humans while probing for small blood vessels in the skin. DENV causes the most prevalent arthropod-borne viral disease in humans, yet no vaccine or specific therapeutic is currently licensed. Although primary DENV infection confers life-long protective immunity against re-infection with the same DENV serotype, secondary infection with a different DENV serotype can lead to increased disease severity via cross-reactive T-cells or enhancing antibodies. This review summarizes recent findings in humans and animal models about DENV infection of DCs, monocytes, and macrophages. We discuss the dual role of DCs as both targets of DENV replication and mediators of innate and adaptive immunity, and summarize immune evasion strategies whereby DENV impairs the function of infected DCs. We suggest that DCs play a key role in priming DENV-specific neutralizing or potentially harmful memory B- and T-cell responses, and that future DC-directed therapies may help induce protective memory responses and reduce dengue pathogenesis.