Human effector B lymphocytes express ARID3a and secrete interferon alpha☆
Graphical abstract
Introduction
Previously, we found that constitutive expression of the transcription factor A-T rich interacting domain 3a (ARID3a) in murine B cells led to the development of anti-nuclear antibodies [1], [2], a common phenotype of the autoimmune disease systemic lupus erythematosus (SLE). While most circulating peripheral blood B lymphocytes fail to express ARID3a in healthy persons, we found that numbers of ARID3a+ B lymphocytes were dramatically increased (up to >40-fold) in SLE patients [3]. Importantly, elevated numbers of ARID3a-expressing B cells were associated with increased disease activity and varied over time in association with SLE disease activity index scores [3]. These data suggested a potential role for ARID3a in SLE disease pathogenesis. To date, there is not a unifying biomarker predictive of susceptibility or disease activity among SLE patients [4].
Approximately half of SLE patients exhibit increased levels of the cytokine interferon alpha (IFNa), and these levels have been associated with inflammation and disease activity in SLE [5], [6], [7]. Elevated IFNa levels result in increased expression of multiple IFN-responsive genes in SLE peripheral blood cells, collectively referred to as an “interferon signature” [8], [9]. Although the mechanisms which initiate IFN signatures in SLE remain elusive, plasmacytoid dendritic cells (pDCs) are thought to be the primary cells responsible for secreting IFNa [reviewed in Ref. [10]].
In the last decade, several investigators reported that B lymphocytes can act as cytokine producing effector B cells that modulate activities of other cell types during an immune response [reviewed in Refs. [11], [12]]. B cell effector functions were highlighted when SLE patients receiving B cell depleting therapy lessened disease activity without changes in autoantibody levels [13]. B cells responding to toll-like receptors (TLR) ligands produce an array of cytokines as B effector cells, including IFNγ, IL-12, IL-2, TNF-α, and IL-6 [14]. However, IFNa production by B cells has been understudied. Although B cells infected with the Epstein-Barr virus (EBV) express IFNa [15], little is known regarding IFNa production by human primary B cells.
Because our data indicated a strong association between numbers of ARID3a+ B lymphocytes and increased disease activity, we asked how ARID3a expression contributes to autoimmunity in SLE. Intriguingly, we observed no direct correlation between ARID3a expression in human SLE B cells and autoantibody production [16]. Therefore, we hypothesized that the relationship between ARID3a+ B cells and disease activity was antibody-independent, and might be associated with inflammatory responses that lead to “interferon signatures” observed in SLE [5].
Section snippets
Participants
Peripheral blood mononuclear cells from a total of 22 SLE patients and 11 healthy controls were analyzed for ARID3a expression. SLE samples were defined as ARID3aH if numbers of ARID3A+ B cells >2 standard deviations above the average numbers of ARID3a+ B cells in healthy controls (9,830 ARID3a+ B cells/ml), or ARID3aN, if numbers of ARID3a+ B cells were similar to healthy controls, as previously described [3].
Plasma assessment
Due to low IFNa levels in peripheral blood, ELISA-based methods for quantitation can
ARID3a is associated with IFNa expression
We postulated that ARID3a over-expression in SLE might be associated with differential gene regulation in total PBMCs. Because we found that numbers of cells expressing ARID3a in individuals vary over time, division of SLE samples based on total numbers of ARID3a+ B cells allowed us to better evaluate phenotypes directly associated with ARID3a expression [3]. Others have shown differential methylation patterns in SLE PBMCs compared to PBMCs from healthy controls [24], [25]. We hypothesized that
Discussion
We now show that expanded numbers of ARID3a+ B cells in SLE are associated with increased plasma levels of IFNa. SLE B cells that express ARID3a synthesize IFNa, and express increased levels of IFNa signature genes previously associated with lupus disease activity [38]. In addition, our data indicate that the TLR 9 agonist CpG induces ARID3a expression and IFNa production in healthy donor B lymphocytes. Furthermore, both SLE ARID3a+ B cells and healthy donor ARID3a+ MZ-like B cells secrete
Disclosure statement
The authors declare that there are no competing financial interests.
Acknowledgements
The authors wish to thank T. D. Templeton and V. Roberts for technical assistance, Drs. S. Kovats, D. Farris, and M. Coggeshall for reagents, and Drs. TF Tedder and MB Humphrey for helpful discussions. Funding was provided by the Lupus Foundation of America (CFW), and grants from the National Institutes of Health: AI090343 and AI044215 (CFW), and AR053483, GM103510, AI101934, AI082714, GM104938 (JMG, JAJ), and AR056360, AR063124, and GM110766 (PMG).
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2019, Journal of AutoimmunityCitation Excerpt :However, in B lymphocytes, developmentally less mature cells expressed ARID3a without IFNα, and induction of ARID3a transcripts occurred prior to detection of IFNα transcripts [8]. Furthermore, inhibition of ARID3a in a B cell line also inhibited IFNα expression [8]. Regardless of which protein is upstream in pDCs and LDNs, a large number of genes appear to be co-regulated in correlation with ARID3a and IFNα.
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2018, Dubois' Lupus Erythematosus and Related SyndromesExpression and methylation data from SLE patient and healthy control blood samples subdivided with respect to ARID3a levels
2016, Data in BriefCitation Excerpt :Methyl-seq data from SLE PBMCs segregated based on high or normal numbers of ARID3a+ B cells was deposited in NCBI׳s GEO database under the following accession number GEO: GSE84965 [2]. Tables 1 and 2 show qRT-PCR data obtained via Biomark HD for Type I IFN pathway genes from RNA derived from SLE B cells subdivided based on ARID3a levels [1], and for healthy control B cells with or without CpG induced ARID3a expression [4]. IFN signature genes are in bold.
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Ward et al. identified a new human effector B lymphocyte characterized by expression of the transcription factor ARID3a and type I interferon. Increased numbers of ARID3a+ B lymphocytes in lupus patients were associated with inflammatory responses and interferon production. These data implicate ARID3a+ B cells as therapeutic targets in SLE.