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Objectives: An important pathogenic role for neutrophils in systemic lupus erythematosus (SLE) has been proposed. Neutrophils that lack brain and muscle aryl hydrocarbon receptor nuclear translocator-like 1 ( Bmal1 ), one of the clock genes, are defective in aging and proinflammatory responses. We assessed the role of Bmal1 in clinical and immunologic manifestations of murine lupus and in human SLE neutrophils., Methods: Myeloid-conditional Bmal1 knockout mice ( Bmal1 Mye-/- ) and wild type (WT) were treated with epicutaneous TLR7/8 agonist (imiquimod; IMQ) for 6 weeks to induce a lupus phenotype. Upon euthanasia, immune responses, autoantibodies and renal manifestations were evaluated. NET formation and gene expression of bone marrow (BM)-derived murine neutrophils were evaluated. BMAL1 expression was quantified in SLE neutrophils and compared with clinical disease., Results: IMQ-treated Bmal1 Mye-/- and WT displayed comparable systemic inflammation. While renal function did not differ, serum anti-dsDNA levels and renal immune complex deposition were significantly increased in Bmal1 Mye-/- . While no differences were observed in NET formation, expression levels of April in BM neutrophils were significantly higher in Bmal1 Mye-/- . Bulk RNA-sequence data showed that BM neutrophils in IMQ-treated Bmal1 Mye-/- were relatively immature when compared with IMQ-treated WT. BM showed an enhanced April protein expression in Bmal1 Mye-/- mice. BMAL1 levels in human SLE peripheral blood neutrophils correlated positively with serum C3 and negatively with serum anti-dsDNA levels., Conclusion: Bmal1 is associated with lower disease activity in SLE. These results indicate that perturbation in the circadian rhythm of neutrophils can have pathogenic consequences in SLE., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Nakabo, Sandoval-Heglund, Hanata, Brooks, Hoffmann, Zhang, Ambler, Manna, Poncio, Hasni, Islam, Dell’Orso and Kaplan.)

A distinct B cell population marked by elevated CD11c expression is found in patients with systemic lupus erythematosus (SLE). Cells with a similar phenotype have been described during chronic infection, but variable gating strategies and nomenclature have led to uncertainty of their relationship to each other. We isolated CD11c hi cells from peripheral blood and characterized them using transcriptome and IgH repertoire analyses. Gene expression data revealed the CD11c hi IgD + and IgD - subsets were highly similar to each other, but distinct from naive, memory, and plasma cell subsets. Although CD11c hi B cells were enriched in some germinal center (GC) transcripts and expressed numerous negative regulators of B cell receptor (BCR) activation, they were distinct from GC B cells. Gene expression patterns from SLE CD11c hi B cells were shared with other human diseases, but not with mouse age-associated B cells. IgH V-gene sequencing analysis showed IgD + and IgD - CD11c hi B cells had somatic hypermutation and were clonally related to each other and to conventional memory and plasma cells. However, the IgH repertoires expressed by the different subsets suggested that defects in negative selection during GC transit could contribute to autoimmunity. The results portray a pervasive B cell population that accumulates during autoimmunity and chronic infection and is refractory to BCR signaling., Competing Interests: MDC, PB, ACG, and PEL are employed by AMPEL BioSolutions, LLC. VK is a full-time employee and shareholder of AstraZeneca. RE and SWare full time employees and shareholders of Viela Bio, and shareholders of AstraZeneca. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Maul, Catalina, Kumar, Bachali, Grammer, Wang, Yang, Hasni, Ettinger, Lipsky and Gearhart.)

Autoantibodies directed against citrullinated epitopes of proteins are highly diagnostic of rheumatoid arthritis (RA), and elevated levels of protein citrullination can be found in the joints of patients with RA. Calcium-dependent peptidyl-arginine deiminases (PAD) are the enzymes responsible for citrullination. PAD2 and PAD4 are enriched in neutrophils and likely drive citrullination under inflammatory conditions. PADs may be released during NETosis or cell death, but the mechanisms responsible for PAD activity under physiological conditions have not been fully elucidated. To understand how PADs citrullinate extracellular proteins, we investigated the cellular localization and activity of PAD2 and PAD4, and we report that viable neutrophils from healthy donors have active PAD4 exposed on their surface and spontaneously secrete PAD2. Neutrophil activation by some stimulatory agents increased the levels of immunoreactive PAD4 on the cell surface, and some stimuli reduced PAD2 secretion. Our data indicate that live neutrophils have the inherent capacity to express active extracellular PADs. These novel pathways are distinguished from intracellular PAD activation during NETosis and calcium influx-mediated hypercitrullination. Our study implies that extracellular PADs may have a physiological role under non-pathogenic conditions as well as a pathological role in RA.