Neutrophilia is a hallmark of adult-onset Still's disease (AOSD). This study aimed to investigate the role of a distinct subset of granulocytes, the low-density granulocytes (LDGs) in the pathogenesis of AOSD.
A total of 56 patients with AOSD were included in the study. LDGs were quantified by flow cytometry. Correlations between LDGs with disease activity and laboratory parameters were determined by Spearman's nonparametric test. The cellular sources of the pro-inflammatory cytokines in AOSD were determined by intracellular staining.
Active AOSD patients displayed significantly higher levels of LDGs compared with inactive AOSD patients and healthy controls (HCs) (P<0.001). Circulating LDGs were significantly correlated with CRP, ESR and the modified Pouchot score in patients with AOSD (P<0.01). The levels of LDGs were significantly decreased after the active AOSD patients achieved disease remission (P=0.0391). CD14+ monocytes constituted over 90% IL-1β+ peripheral blood mononuclear cells (PBMCs) and over 80% TNF-α+ PBMCs in both active AOSD patients and HCs, respectively. In active AOSD, CD14+ monocytes accounted for 24.6% to 75.0% of IL-6+ PBMCs, while LDGs comprised 22.8% to 72.2% of IL-6+ PBMCs. In contrast, over 90% IL-6+ PBMCs were CD14+ monocytes in HCs. A significant correlation was identified between the levels of LDGs and serum IL-6 levels in AOSD (P<0.0001).
Active AOSD is associated with elevated levels of a pro-inflammatory subset of neutrophils, the LDGs that produce IL-6. Our data highlight an unappreciated role of LDGs in the aberrant innate immune responses in AOSD.