A 23bp Indel Polymorphism in TLR2 Gene Enhances Inflammation and Disease Severity in Dengue

Abstract

Background. Dengue is the most rapidly spreading viral disease transmitted by the bite of infected Aedes mosquitos. Pathogenesis of dengue is still unclear; although host genetic factors, immune responses and virus serotypes have been proposed to contribute to disease severity. The development of high-throughput methods have allowed to scale up capabilities of identifying the key markers of inflammation. Since NS1 protein of dengue virus has been reported to activate immune cells towards enhanced inflammation through TLR2, we examined the role of a polymorphism, a 23bp deletion in 5'UTR region of TLR2 gene in patients with dengue (with and without warning signs) and correlated with plasma levels of inflammatory mediators with disease severity and viral serotypes. Methods: Eighty nine patients classified as per WHO 2009 criteria during dengue outbreak in Odisha, India in 2016 were included in the current study. Presence of dengue virus (DENV) was demonstrated by detecting NS1 antigen, IgM capture ELISA and serotypes in circulation were discriminated by type-specific RT-PCR and/or sequencing. Sixty-one confirmed dengue cases were typed for TLR2 indel polymorphism and compared with 485 disease free controls. Plasma samples were assayed for 41-plex cytokine/ chemokines using Luminex bead based immunoassay. Results: Presence of 23bp deletion allele of TLR2 gene was significantly more in patients with severe dengue in comparison to dengue fever cases (p= 0.03; Odds ratio 4.05) although the frequency of insertion (Ins) allele of TLR2 was comparable in healthy controls and dengue cases (82.4 and 87.9 % respectively). Seventy-three (82%) samples were found to be positive by NS1/ IgM capture ELISA/ RT-PCR. DENV-2 was predominant (58%) during the outbreak. Among the host inflammatory biomarkers 9 molecules were significantly altered in dengue patients when compared to healthy controls. The increased levels of IFN-γ, GM-CSF, IL-10, IL-1Rα and MIP-1β correlated significantly with severe dengue. Conclusions:The frequency of 23bp Indel mutation of TLR2 was comparable between healthy controls and dengue fever (with and without warning signs), suggesting that this indel mutation does not contribute significantly to susceptibility/ resistance to dengue; however, del allele of TLR2 gene was significantly more associated in patients with severe dengue symptoms when compared to dengue fever cases. INTRODUCTIONDengue virus transmitted by Aedes mosquito, is an increasing global problem, with an estimate of 390 million infections per year and about 3.6 billion people at risk to dengue. India alone contributed to 34% of the total global infections (Bhatt et al 2013). Infection with the dengue virus (DENV) resulted with a spectrum of clinical manifestations ranging from asymptomatic infection, self-limiting, dengue fever (DF) with or without warning signs or to life threatening severe There are four antigenically related but distinct serotypes of this virus, described as DENV-1, DENV-2, DENV-3, and DENV-4. The dengue virus is a positive ...

Dengue Immunopathogenesis: A Crosstalk between Host and Viral Factors Leading to Disease: PART II - DENV Infection, Adaptive Immune Responses, and NS1 Pathogenesis

“…In humans, increased levels of many of these soluble factors including IFN-γ, TNF-α, IL-1β, IL-4, IL-6, IL-7, IL-10, IL-13, IL-15, IL-17, IL-18, macrophage migration inhibitory factor (MIF), chemokines such as IL-8, CCL2, CCL4, CCL5, CXCL10 (IP-10) and the monocyte chemoattractant protein-1 (MCP-1) have been reported in patients with DHF when compared to DF [1,10,[152][153][154]. Studies show that elevated levels of IL-6, IL-10, IFN-γ, MIF, and CCL-4 could be used as potential biomarkers of severe dengue [155,156].…”