Background/Purpose: Neutrophil (PMN) activation and neutrophil extracellular trap (NET) formation are implicated in the pathogenesis of Systemic Lupus Erythematosus (SLE), particularly in the acceleration of organ and vascular damage. Lupus neutrophils can drive B-cell activation and auto-antibody (Ab) production, at least in part, by production of type-I interferons and B-cell activating factor (BAFF) and, by exposing self-antigens (Ags), such as oxidized mitochondrial DNA and cardiolipin. The presence of anti-cardiolipin Abs in SLE patients has been associated with an increased risk of cardiovascular events due to atherosclerosis. Still, little is known about the potential link between neutrophil abnormalities, B-cell activation, and auto-Ab production. This study was undertaken to test whether PMN activation and NET formation contribute to increased BAFF levels and auto-Ab production in SLE patients.

Methods: BAFF levels were analyzed in serum samples from 60 SLE patients with varying levels of disease activity and 20 healthy controls (HC) by ELISA. Plasma levels of NETs and 8-OHdG were measured by ELISA. Anti-dsDNA titers complement and CRP levels were obtained from clinical records. Autoantibody reactivities were assessed by microarray.

Results: Mean BAFF levels were significantly higher in SLE patients, as compared to HC (2785.25 vs 924.29 pg/mL, p< 0.0001). After defining a cut-off for BAFF levels at 1429.4 pg/mL (mean + 3_SD HC), around 60% of SLE patients were identified to have elevated BAFF levels. No associations between BAFF titers and gender, ethnicity, and age at diagnosis were found. Although BAFF levels did not associate significantly with the overall SLEDAI scores, we found a significant correlation between BAFF levels and increased CRP levels, and decreased serum C3 and C4 levels, suggesting an association with ongoing immune complex (IC)-driven disease. Compatible with this hypothesis, levels of ICs, measured by an in vitro assay, correlated with BAFF levels (r=0.38, p=0.02). Asking if BAFF levels correlated with neutrophil activation, we observed that serum-mediated neutrophil activation, as well as the cell-free 8-OHdG DNA, an inflammatory NET-derived component, both correlated with BAFF levels (r=0.34, p<0.05 for both analyses), consistent with PMN activation contributing to elevated BAFF levels in SLE. Microarray data revealed positive correlations between BAFF levels and IgG autoreactivity against M2-mitochondrial antigen, sphingomyelin, phosphatidylinositol, β2 glycoprotein and cardiolipin.

Conclusion: We found an association between heightened BAFF production and markers of PMN activation and particularly increased levels of inflammatory oxidized DNA, compatible with the release of BAFF during NETosis. Our data support the hypothesis that neutrophils, through IC-mediated activation, release BAFF as well as key auto-Ags such as dsDNA and mitochondrial components, including cardiolipin, which may contribute to the production of pathogenic auto-Abs. These results provide new insights into how neutrophils and BAFF may contribute to the development of cardiovascular disease and help identify new effective therapies for SLE patients.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/increased-levels-of-baff-in-sle-patients-correlates-with-neutrophil-activation-and-autoantibody-production/