Background/Purpose:

Systemic Lupus Erythematosus (SLE) is a systemic autoimmune disease characterized by immune dysfunction and autoantibody production. In addition to the adaptive immune system, neutrophils likely also play an important role in SLE pathogenesis. Neutrophils are terminally differentiated cells and are highly sensitive to environmental cues, including infections, sterile inflammation and medication. This study examined whether the increased levels of inflammatory cytokines in SLE induce neutrophil activation and whether the regulation of neutrophil function differs in SLE patients compared to controls.

Methods:

Neutrophils from 19 SLE patients with varying disease activity and 11 controls were enriched by dextran sedimentation and density gradient centrifugation. Basal and stimulated levels of activation marker L-selectin (CD62L) and exocytosis marker CD66b were measured by flow cytometry. Percentage of cells with neutrophil extracellular traps (NET) were determined by microscopy. Plasma cytokines were measured by xMAP assays. Expression of mRNA and microRNA were determined by quantitative PCRs.

Results:

Basal levels of CD62L were not different between SLE patients and controls; however, upon stimulation with TLR7/8 ligand, SLE patients showed reduced activation compared to controls (p < 0.0001). The CD62L levels negatively correlated with inflammatory cytokines IL1β (r =-0.7866, p =0.0094), IL23 (r = -0.845, p = 0.0033), IL6 (r =-0.75, p = 0.0159), MIP1α (r = -0.8424, p =0.0037), TNF β (r = -0.7091, p =0.0268) in controls, suggesting increased downregulation of CD62L or increased activation of neutrophils due to exposure to inflammatory mediators. No correlation between these cytokines and CD62L levels were observed in SLE. CD66b levels were significantly lower in SLE patients compared to controls (p = 0.0030). In this small cohort, no significant differences between basal levels of NET forming cells between SLE and controls were found. However, CD66b levels in SLE patients, but not in controls, positively correlated with the percentage of netting neutrophils (r =0.5858, p =0.015), suggesting a role for reactive oxygen species in NET formation in SLE. CD66b levels in SLE patients negatively correlated with BAFF (r = -0.4848, p =0.0354), while the levels in controls did not correlate with plasma cytokines. Fold changes in surface markers upon stimulation with formyl peptide were similar between SLE and controls. The levels of surface markers on SLE neutrophils were not influenced by prednisone or hydroxychloroquine use. SLE neutrophils had significantly higher levels of genes involved in NFkB signaling and lower levels of micro RNA miR223 and miR27a, suggesting hypersensitivity to infectious stimuli and reduced apoptosis.

Conclusion:

SLE neutrophils had higher activation thresholds for mediators of sterile inflammation. Our data suggest that the regulation of neutrophil responses in SLE may be through pathways distinct from those in unaffected individuals, although the neutrophils maintain their ability to respond to external stimuli.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/regulation-of-neutrophil-activation-in-systemic-lupus-erythematosus/