Extracellular traps in peripheral blood mononuclear cell fraction, a proposed biomarker for childhood-onset systemic lupus erythematosus

Abstract

Abstract Although the utilization of low-density granulocytes (LDGs) and neutrophil extracellular traps (NETs) for the determination of lupus disease severity are mentioned, data from pediatric lupus are still very less. Then, 46 patients with childhood-onset systemic lupus erythematosus (83% females, mean age 15 ± 0.2 years) with 26 and 20 cases with normal and low complement, respectively, and 20 adult normal volunteers were analyzed. The parameters that could differentiate normal volunteers from lupus and between low versus normal complement lupus were serum IFN-α, serum CitH3 (citrullinated histone 3), and extracellular traps (ETs) in LDGs but not NETs (from regular-density neutrophils), LDGs or other parameters (such as endotoxemia, other cytokines, and serum dsDNA). Adding lipopolysaccharide (LPS) in LDGs further induced ETs in both low and normal complement groups indicating a property of inducible ETs. The activation by recombinant IFN-α or dsDNA in isolated neutrophils from adult healthy volunteers turns into LDGs (isolated by gradient separation after the induction) and NETs (from the LDGs portion as determined by immunofluorescent analysis using CitH3, myeloperoxidase, and neutrophil elastase staining) at 45 min and 3 h post-stimulation, respectively. At 3 h post-stimulation, approximately half of the LDGs turn into late apoptosis cells as evaluated by flow cytometry analysis. The expression of CD66b (an adhesion molecule) in LDGs induced by IFN-α or dsDNA was similarly more prominent than the regular-density neutrophils indicating a more profound activity of LDGs. In conclusion, LDGs in lupus might be induced by IFN-α and/or dsDNA in patients with lupus which might be in the process of cell death through NETosis and apoptosis (the exacerbating processes of lupus disease activity). Although LDGs could not differentiate low versus normal complement lupus, the ETs in LDGs might be useful as another biomarker of disease activity in pediatric lupus. More studies are interesting.