Abstract
Dengue virus is a major global health threat and can lead to life-threatening hemorrhagic complications due to immune activation and cytokine production. Cross-reactive antibodies to an earlier dengue virus infection are a recognized risk factor for severe disease. These antibodies bind heterologous dengue serotypes and enhance infection into Fc-receptor-bearing cells, a process known as antibody-dependent enhancement of infection. One crucial cytokine seen elevated in severe dengue patients is IL-1β, a potent inflammatory cytokine matured by the inflammasome. We used a highly-physiologic system by studying antibody-dependent enhancement of IL-1β in primary human monocytes with anti-dengue human monoclonal antibodies isolated from patients. Antibody-enhancement increased viral replication in primary human monocytes inoculated with supernatant harvested from Vero cells infected with dengue virus serotype 2 (DENV-2) 16681. Surprisingly, IL-1β secretion induced by infectious supernatant harvested from two independent Vero cell lines was not enhanced by antibody. Secretion of multiple other inflammatory cytokines was also independent of antibody signaling. However, IL-1β secretion did require NLRP3 and caspase-1 activity. Immunodepletion of dengue virions from the infectious supernatant confirmed that virus was not the main IL-1β-inducing agent, suggesting that a supernatant component(s) not associated with the virion induced IL-1β production. We excluded RNA, DNA, contaminating LPS, viral NS1 protein, complement, and cytokines. In contrast, purified Vero-derived DENV-2 16681 exhibited antibody-enhancement of both infection and IL-1β induction. Furthermore, C6/36 mosquito cells did not produce such an inflammatory component, as crude supernatant harvested from insect cells infected with DENV-2 16681 induced antibody-dependent IL-1β secretion. This study indicates that Vero cells infected with DENV-2 16681 may produce inflammatory components during dengue virus propagation that mask the virus-specific immune response. Thus, the choice of host cell and viral purity should be carefully considered, while insect-derived virus represents a system that elicits antibody-dependent cytokine responses to dengue virus with fewer confounding issues.
Highlights
With an estimated 390 million global infections per year, dengue virus (DENV) is the most burdensome arbovirus in the world [1]
Mobilized peripheral blood mononuclear cells (PBMCs) were isolated from leukapheresed blood and inoculated with a multiplicity of infection (MOI) of 50 focus-forming units of dengue virus serotype 2 (DENV-2) strain 16681 that had been incubated with 1 μg/ml anti-DENV prM human monoclonal antibody 5G22
Vero cells are highly susceptible to DENV infection, while monocytes are very resistant to the virus
Summary
With an estimated 390 million global infections per year, dengue virus (DENV) is the most burdensome arbovirus in the world [1]. A first infection with any serotype may cause an asymptomatic infection or a mild to severe flulike illness referred to as dengue fever (DF) [3]. Patients typically recover without complication and develop longterm immunity to the same DENV serotype, but immunity to heterologous serotypes is transient [4, 5]. Upon later infection with a second serotype of DENV, a small percentage of patients progress to the life-threatening disease course of severe dengue [2, 4]. A reversible permeability develops in the vasculature, causing hemorrhagic manifestations and potential hypovolemic shock [3, 6]. There is no specific cure or vaccine, but supportive therapy until the disease course passes can reduce mortality levels from greater than 20% to less than 1% [2, 7]
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