Dengue NS1 induces phospholipase A2 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 IFN alpha level was significantly higher (p = 0.013) only at 12 h. IL-1 beta (p = 0.028 and p = 0.031) and TNF alpha (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.

Automated summary

This study found that the NS1 protein of the dengue virus can induce the production of PLA2 enzymes, leading to the release of prostaglandins and inflammatory cytokines, which may contribute to the pathogenesis of dengue.