Dengue Infection - Recent Advances in Disease Pathogenesis in the Era of COVID-19

Abstract

The dynamics of host-virus interactions, and impairment of the host's immune surveillance by dengue virus (DENV) serotypes largely remain ambiguous. Several experimental and preclinical studies have demonstrated how the virus brings about severe disease by activating immune cells and other key elements of the inflammatory cascade. Plasmablasts are activated during primary and secondary infections, and play a determinative role in severe dengue. The cross-reactivity of DENV immune responses with other flaviviruses can have implications both for cross-protection and severity of disease. The consequences of a cross-reactivity between DENV and anti-SARS-CoV-2 responses are highly relevant in endemic areas. Here, we review the latest progress in the understanding of dengue immunopathogenesis and provide suggestions to the development of target strategies against dengue.

Keywords: COVID-19; antibody-dependent enhancement (ADE); cytokine storm; dengue (DENV); endothelial dysfunction; inflammasome; pathogenesis; plasmablasts.

Figure 1

Original antigenic sin and antibody-dependent enhancement in DENV infection. (A) When primary infection occurs with e,g. DENV1, resulting in activation of adaptive immune responses (both T and B cells) DENV1-specific T cells are selected, activated, and clonally expanded to combat infection. Upon termination of primary infection, memory DENV1–specific T cells and B cells are formed and are retained with higher frequency compared to other naïve cells. (B) A secondary infection with the same serotype of DENV (e.g. DENV1) for the second time (homotypic infection), the virus will evoke a memory response that entails in the effective containment of DENV1 by highly specific T and B cell responses. (C) A secondary challenge with a different serotype of DENV (e.g. DENV2) (heterotypic infection), there is a chance that the cross-reactive memory T and B cells get preferentially activated, proliferated over the DENV2-specific T and B cells. The cross-reactive DENV1–specific adaptive immune responses outcompete naïve T cells that would be more specific for DENV2, resulting in an expanded memory T cell pool that is of low specificity for DENV2 and poor viral clearance. Antibody-dependent enhanced replication also has the potential to occur during a secondary, heterologous infection.

Figure 2

Proposed mechanism of evasion of DENV and DENV-infected cells from classical and lectin pathway-mediated complement attack in the host. NS1 protein released by DENV-infected cells activates the classical pathway of complement activation resulting in the formation of a tri-partite C1S-NS1-C4 complex. C4 undergoes enzymatic cleavage forming C4a (anaphylatoxin and chemotaxin) and C4b present in the fluid phase becomes susceptible to spontaneous hydrolysis attributing to paucity of C4 in the circulation (33). NS1 recruits C4BP and binds with it leading to subsequent recruitment of C4b to engage with the NS1-C4BP complex to allow the ‘stepping-in’ of factor I. Factor I is a negative regulator of complement activation that cleaves C4b into C4c and C4d fragments to limit the classical as well as the lectin pathways (34). Competitive binding of NS1 to MBL prevents recognition of DENV by MBL that protects DENV from neutralization by MBL.

Figure 3

T-dependent and T-independent plasmablast reactions elicited by dengue infection. Dengue virus infection activates B cells directly or indirectly, expanding the B cells into a vast number of circulating plasmablasts. Plasmablasts that are derived from extracellular B cells proliferate rapidly in an innate manner without the requirement of T cell help. The Immunoglobulin gene of this plasmablast population is hypomutated as it lacks germinal centre reaction and produces IgM, IgG and IgA. T-independent plasmablasts response vigorously during acute dengue infection regardless of primary or secondary infection. On the other hand, follicular B cells activated receive help from follicular helper T cells (T_FH) and initiate the germinal centre reaction where clonal expansion, class switch and active somatic hypermutation (SHM) occurred. The plasmablast produced are long lived and predominant antibodies released are of IgG isotype. Surprisingly, these plasmablasts with evidence of T cell help secrete poor levels of antibodies compared to those without T cell help, but present with high oxidative phosphorylation, eukaryotic initiation factor (EIF2) pathway, and mitochondrial dysfunction. Memory B cells generated following dengue infection provides long term protection after recovery.

Figure 4

Interplay between NS1, inflammasome activation, complement activation, autoreactive antibodies and cytokine storm in endothelial dysfunction. 1) DENV and NS1 can directly activate CS, the excessive conversion of C3, C4 and C5 to their active forms C3b, C4b and C5b will inevitably cause increased level of C3a, C4a and C5a (anaphylatoxin). Large amount of anaphylatoxin will cause aberrant activation of mast cells and release massive amount of histamine, along with other pro-inflammatory cytokines, leading to increase of the vascular permeability and vascular leakage. 2) anti-NS1-specific IgM and IgG have been found circulating in the blood stream forming immune complexes with the both forms of NS1 proteins. While mNS1 is expressed on DENV infected cells, the circulating sNS1 can subsequently bind to surface of infected or uninfected cells via heparan sulfate and chondroitin sulfate E (90). These antibodies will then bind to NS1 and leading complement-dependent lysis of cell and antibody-dependent cellular cytotoxicity, damaging the endothelial layer and leading to vascular leakage (47). 3) Secretion of IL-1β, IL-18 and HMGB1 results from NLRP3 inflammasome activation. 4) In the circulation, IL-1β and IL-18 binds to their cognate receptors (IL-1R1/acP and IL-18Rα/β) expressed on the surface of endothelial cells to activate intracellular signaling molecules, involving MyD88, IL-1 receptor-associated kinase 1/4 (IRAK1/4), and TNF receptor-associated factor (TRAF), which entails in NF-κB activation. NS1 can also activate the NF-κB signaling pathway via TLR4. The activation of NF-κB signaling pathway increases the secretion of pro-inflammatory cytokines and chemokines to mediate leukocyte adhesion and extravasation (diapedesis). Additionally, the binding of HMGB1 to the RAGE receptor leads to the downstream activation of p38 MAP kinase, resulting in phosphorylation of the actin-binding protein Hsp27 and caldesmon, which causes actin stress fibers to form, cytoskeletal remodeling, and endothelial contraction. All these reactions increase endothelial permeability by altering cell contractility and disruption of intercellular junctions. Given the ability of IL-18 to induce the production of various pro-inflammatory mediators including TLR4 and RAGE via activation of NFκ-B signaling (75, 91, 92), their higher expression will condition the endothelial cells to be more responsive to stimulation by NS1 and HMGB1, to further magnify inflammation and vascular permeability.