Low-density granulocytes and neutrophil extracellular traps in dengue, impacts of interferon alpha and cell-free DNA

The activation of neutrophils by cytokines and cell-free DNA might precede hemoconcentration in dengue. Then, the neutrophil extracellular traps (NETs) and the neutrophils in the peripheral blood mononuclear cell (PBMC) fraction, referred to as low-density granulocytes (LDGs), were explored. The blood samples at 5 days of fever from patients with dengue were collected and categorized into dengue without and with warning signs (DWoWS and DWWS). Meanwhile, the patients with hemoconcentration were excluded. The NET-associated parameters, as determined by serum cell-free DNA and the fluorescent staining in the polymorphonuclear (PMN) fraction, in the DWWS group (n = 31) were higher than in DWoWS (n = 40). Meanwhile, complete blood count, serum cytokines (IFN-α, TNF-α, and IL-6), and LDGs were not different. The extracellular traps (ETs), stained by neutrophil elastase (NE) and myeloperoxidase (MPO), in the PBMC fraction of the DWWS group were higher than in DWoWS, while the ETs were non-detectable in healthy volunteers. The recombinant IFN-α and cell-free DNA reduced the density of regular neutrophils isolated from healthy volunteers into LDGs (measured by gradient separation) and also induced NETs (evaluated by NE and MPO co-expression). Meanwhile, CD66b (an adhesion molecule) and apoptosis in these LDGs were more prominent than in regular neutrophils. The NETs and LDGs presented in blood samples of patients with dengue might be due to the activation by IFN-α and cell-free DNA. However, only NETs could differentiate DWWS from DWoWS. Further studies to use NETs and LDGs in clinical practice are interesting.