Session Type: Abstract Submissions (ACR)
Background/Purpose: Although SLE is known to be associated with a type I interferon signature in the peripheral blood, the precise site and mechanism of IFN pathway activation in SLE remain unclear. Given that IFN can impair B cell development in murine bone marrow (BM), we asked whether IFN activation is present in SLE BM and its potential consequences for disease pathogenesis.
Methods: The IFN signature was assessed in BM of SLE patients (n=28) and normal controls (NC, n=20) by examining the relative expression of 3 IFN inducible genes IFIT1, IRF7, and G1P2 by qPCR. Neutrophils were isolated using Percoll density gradient and phenotype confirmed by flow cytometry. Type I IFN, BAFF, and APRIL expression in total aspirates and purified neutrophils was measured by qPCR normalized to GAPDH. Neutrophil expression of BAFF and APRIL was confirmed by immunofluorescence. NZM2328 lupus prone female mice (pre-disease 12 wk) were compared to Balb/c (n=7 per group) for Type I IFN activation and production and secretion of cytokines that may alter B cell development. B cells were defined by flow cytometry using standard markers.
Results: The majority of SLE patients (57%) had an IFN signature in the BM that was more pronounced than the paired peripheral blood (PB) and associated with both higher autoantibodies and disease activity (BM vs. PB for IFN high group compared to NC: 45.7-fold vs. 18.5-fold, p=0.0009 for G1P2; 108.5-fold vs. 54-fold, p=0.005 for IFIT1). There was also a significantly higher expression of BAFF and APRIL in the IFN high SLE BM aspirates (BAFF: 2.45+/-0.66 fold compared to NC; APRIL: 6.04+/-2.5, p=0.01). BM neutrophils in SLE showed a significantly higher expression of APRIL and IFNα when compared to NC BM (p=0.04) and also a correlation between IFNα expression and APRIL (p=0.0004) and BAFF expression (p=0.0001), suggesting that IFNa may be driving APRIL and BAFF. SLE IFN high patients had profound alterations in the BM B cell compartment with significant reductions in precursor B cells (p=0.02) but increases in transitional B cells (27%, 4.6%, and 7.5% T1/T2 in IFN high SLE, IFN low SLE and NC, respectively; p=0.013). Lupus prone mice had similar alterations in B cell development. Notably, BM neutrophils from lupus mice displayed significant up-regulation of Mx-1 (10-fold, p=0.01), as well as increases in IFNα, IFNb, and BAFF (p=0.03, 0.03, 0.04). In bone sections, we also detected numerous Gr-1+MPO+ neutrophils in NZM mice expressing APRIL and BAFF in close contact with B220+ B cells.
Conclusion: Overall, our results highlight the importance of the BM as a target organ in SLE and provide a previously unappreciated connection between IFN activation, neutrophils, and B cell selection.
This work was supported in part by grants R01 AI077674 (JA), P01 AI078907 (JA), U19 AI56390 Autoimmunity Center of Excellence (JA), R01 HL088419 (MJK), and a Rheumatology Research Foundation Rheumatology Scientist Development Award (JSK).
J. S. Knight,
J. W. Bauer,
M. J. Kaplan,
J. H. Anolik,
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ACR Meeting Abstracts - https://acrabstracts.org/abstract/neutrophil-mediated-interferon-activation-in-systemic-lupus-erythematosus-bone-marrow/