Dengue NS1 induces phospholipase A 2 enzyme activity, prostaglandins, and inflammatory cytokines in monocytes.

Introduction: Dengue virus (DENV) NS1 is a non-structural secretory protein associated with severe disease and known to cause vascular leak leading to dengue haemorrhagic fever (DHF). As phospholipases A ₂ (PLA ₂ ) enzymes, platelet activating factor, and leukotrienes are elevated in dengue, we sought to investigate whether NS1 potentially contributes to disease pathogenesis by inducing PLA ₂ s.
Methods: THP-1 cells and primary human monocytes of healthy adults (n = 6) were co-cultured with DENV1 NS1, LPS and media alone. The latter two were used as positive and negative controls. The cell culture supernatants and lysates were harvested at 12 and 24 h and the activity of secretory and cytoplasmic PLA ₂ , prostaglandins (PGE ₂ and PGD ₂ ) were measured by ELISA and cytokines levels were measured using a magnetic Luminex assay. Expression of PLA2G4A, PLA2G2A, PLA2G5, PLA2G10, PLA2G7, GAPDH, NLRP3 and DDX58 genes were assessed using quantitative RT-PCR.
Results: cPLA ₂ (p = 0.005), sPLA ₂ (p = 0.04), PGE ₂ metabolite (p = 0.02) and PGD ₂ metabolite (p = 0.04) levels were significantly higher at 12 h in monocytes co-cultured with NS1. Levels of IP-10 (p = 0.005) and IL-10 (p = 0.009) was significantly higher at 24 h, whereas IFNα level was significantly higher (p = 0.013) only at 12 h. IL-1β (p = 0.028 and p = 0.031) and TNFα (p = 0.007 and p = 0.011) showed significantly higher levels at both time points. At 12 h significant upregulation of PLA2G4A (p < 0.0001) was seen, whereas PLA2G7 (p = <0.0001), NLRP3 (p = 0.0009) and DDX58 (p = 0.0056) were significantly downregulated. This pattern changed at 24 h with PLA2G4A (p = 0.0069) showing a marked downregulation and PLA2G7, DDX58 and NLRP3 showing an upregulation, although not significant.
Conclusion: Dengue NS1 induces the production of PLA ₂ enzymes, prostaglandins and inflammatory cytokines from primary human monocytes, which could play a role in vascular leak in dengue.
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