Increased development of T-bet+CD11c+ B cells predisposes to lupus in females: Analysis in BXD2 mouse and genetic crosses.

Cardinal features of lupus include elevated B cell activation and autoantibody production with a female sex preponderance. We quantified interactions of sex and genetic variation on the development of autoimmune B-cell phenotypes and autoantibodies in the BXD2 murine model of lupus using a cohort of backcrossed progeny (BXD2 x C57BL/6J) x BXD2. Sex was the key factor leading to increased total IgG, IgG2b, and autoantibodies. The percentage of T-bet+CD11c+ IgD+ activated naive B cells (aNAV) was higher in females and was associated with increased T-bet+CD11c+ IgD- age-related B cells, Fas+GL7+ germinal center B cells, Cxcr5-Icos+ peripheral T-helper cells, and Cxcr5+Icos+ follicular T-helper cells. IFN-ß was elevated in females. Variation in aNAV cells was mapped to Chr 7 in a locus that shows significant interactions between the female sex and heterozygous B/D variant. Our results suggest that activation of naive B cells forms the basis for the female-predominant development of autoantibodies in lupus-susceptible BXD2 mice.

Interrelation of T cell cytokines and autoantibodies in systemic lupus erythematosus: A cross-sectional study.

T-helper cytokines interferon gamma (IFNÉ£), interleukin 17 (IL-17) and IL-10 impact systemic lupus erythematosus (SLE) directly and indirectly via modulation of autoAb production. We determined the separate and combined effects on clinical manifestations of SLE (N = 62). IFNÉ£, IL-17 but not IL-10 were significantly elevated in patients with SLE. IFNÉ£ positively correlated with anti-DNA and anti-SSA. IL-17 positively correlated with anti-SSA and was significantly higher in patients with discoid rash and class V LN. IL-10 did not correlate with circulating autoantibodies but was significantly elevated in patients with LN. Patients with LN had elevated plasma levels of anti-DNA and anti-Sm/ribonuclear protein (RNP). Anti-Sm/RNP levels were decreased in patients with acute mucocutaneous manifestations, including photosensitivity and/or malar rash. The study provides critical insights into pathological mechanisms of LN, which could help guide future diagnoses and therapies.

IL-4 receptor blockade is a global repressor of naïve B cell development and responses in a dupilumab-treated patient.

Here, we report a case of atopic dermatitis (AD) in a patient who received biweekly doses of dupilumab, an antibody against the IL-4 receptor α chain (IL-4Rα). Single cell RNA-sequencing showed that naïve B cells expressed the highest levels of IL4R compared to other B cell subpopulations. Compared to controls, the dupilumab-treated patient exhibited diminished percentages of IL4R+IGHD+ naïve B cells and down-regulation of IL4R, FCER2 (CD23), and IGHD. Dupilumab treatment resulted in upregulation of genes associated with apoptosis and inhibition of B cell receptor signaling and down-regulation of class-switch and memory B cell development genes. The dupilumab-treated patient exhibited a rapid decline in COVID-19 anti-spike and anti-receptor binding domain antibodies between 4 and 8 and 11 months post COVID-19 vaccination. Our data suggest that intact and persistent IL-4 signaling is necessary for maintaining robust survival and development of naïve B cells, and maintaining a long term vaccine response.

IL-4-Induced Quiescence of Resting Naive B Cells Is Disrupted in Systemic Lupus Erythematosus.

Activated naive (aNAV) B cells have been shown to be the precursor of the CD11c+T-bet+ IgD-CD27- double-negative (DN)2 or atypical memory (aMEM) B cells in systemic lupus erythematosus (SLE). To determine factors that maintain resting naive (rNAV) B cells, the transcriptomic program in naive (IGHD+IGHM +) B cells in human healthy control subjects (HC) and subjects with SLE was analyzed by single-cell RNA-sequencing analysis. In HC, naive B cells expressed IL-4 pathway genes, whereas in SLE, naive B cells expressed type I IFN-stimulated genes (ISGs). In HC, aNAV B cells exhibited upregulation of the gene signature of germinal center and classical memory (cMEM) B cells. In contrast, in SLE, aNAV B cells expressed signature genes of aMEM. In vitro exposure of SLE B cells to IL-4 promoted B cell development into CD27+CD38+ plasmablasts/plasma and IgD-CD27+ cMEM B cells. The same treatment blocked the development of CD11c+Tbet+ aNAV and DN2 B cells and preserved DN B cells as CD11c-Tbet- DN1 B cells. Lower expression of IL-4R and increased intracellular IFN-ß in naive B cells was correlated with the accumulation of CD21-IgD- B cells and the development of anti-Smith and anti-DNA autoantibodies in patients with SLE (n = 47). Our results show that IL-4R and type I IFN signaling in naive B cells induce the development of distinct lineages of cMEM versus aMEM B cells, respectively. Furthermore, diminished IL-4R signaling shifted activated B cell development from the DN1 to the DN2 trajectory in patients with SLE. Therapies that enhance IL-4R signaling may be beneficial for ISGhi SLE patients.

Lupus nephritis correlates with B cell interferon-ß, anti-Smith, and anti-DNA: a retrospective study.

BACKGROUND: In systemic lupus erythematosus (SLE), detection of interferon-ß (IFNß) in B cells was found to be most prominent in patients with high anti-Smith (Sm) and renal disease, but a mechanistic connection was not clear. The objective of the present study is to determine the association of IFNß in peripheral blood naïve B cells with the histopathological features of lupus nephritis (LN). METHODS: The percentage of IFNß+ cells in IgD+CD27- naïve CD19+ B cells (B cell IFNß) among peripheral blood mononuclear cells (PBMCs) from 80 SLE patients were analyzed using flow cytometry. Serological and clinical data were collected. The correlations of B cell IFNß with LN classification and with histopathological findings (light, electron, and immunofluorescence [IF] microscopic analyses for deposition of IgM, IgG, IgA, C1q, and C3) were determined in 23 available biopsy specimens. RESULTS: B cell IFNß is positively associated with anti-Sm (p = 0.001), anti-DNA (p = 0.013), and LN (p < 0.001) but was negatively associated with oral/nasal ulcer (p = 0.003) and photosensitivity (p = 0.045). B cell IFNß positively correlated with immune complex (IC) deposit in the glomerular basement membrane (GBM) (p = 0.002) but not in the mesangial (p = 0.107) or tubular region (p = 0.313). Patients with high B cell IFNß had statistically increased development of the proliferative LN (Classes III, IV and/or V), compared to patients with low B cell IFNß (p < 0.0001). Histopathological features positively associated with increased B cell IFNß included active glomerular lesions as determined by fibrocellular crescents (p = 0.023), chronic glomerular lesions indicated by segmental sclerosis (p = 0.033), and a membranous pattern of renal damage indicated by spike/holes (p = 0.015). CONCLUSION: B cell IFNß correlates with history of severe LN, glomerular basement membrane (GBM) IC deposition, and anatomical features of both active and chronic glomerular lesions.

Host Genetics But Not Commensal Microbiota Determines the Initial Development of Systemic Autoimmune Disease in BXD2 Mice.

OBJECTIVE: To determine the extent to which the gut microbiome influences systemic autoimmunity in a mouse model of lupus. METHODS: We generated germ-free (GF) lupus-prone BXD2 mice, which under normal conditions develop spontaneous germinal centers (GCs) and high titers of serum autoantibodies. GF status was confirmed by gut bacterial culture. The autoimmune phenotypes of 6- and 12-month-old gnotobiotic GF BXD2 mice and specific pathogen-free (SPF) BXD2 mice were compared. Serum levels of autoantibodies were measured by enzyme-linked immunosorbent assay. Histologic sections of the mouse kidney and joints were evaluated. Flow cytometry was used to analyze GCs and age-associated B cells. CD4+ T cells were analyzed for PD-1+ICOS+ activated T cells, T follicular regulatory (Tfr) cells (Foxp3+CD25+ PD-1+CXCR5+), and PD-1+ICOS+ T cells expressing interleukin-17A (IL-17A) or interferon-γ (IFNγ) after stimulation with phorbol myristate acetate (PMA)/ionomycin. RESULTS: In 6-month-old mice, GF status did not affect splenomegaly, GC B cells, age-associated B cells, or serum autoantibody levels, except for IgG antihistone. GF BXD2 mice exhibited a significantly higher percentage of Tfr cells compared to their SPF counterparts (P < 0.05). At 12 months of age, however, GF BXD2 mice had significantly diminished IgG autoantibody levels and a lower percentage of GC B cells and age-associated B cells (P < 0.05). Following stimulation with PMA/ionomycin, PD-1+ICOS+ CD4+ T cells expressed significantly lower IL-17A, but not IFNγ, levels in GF BXD2 mice compared to SPF BXD2 mice (P < 0.01). SPF BXD2 mice and GF BXD2 mice developed equivalent renal and joint disease with no significant differences in severity. CONCLUSION: Our results suggest a model in which genetics plays a dominant role in determining the initial development of autoimmunity. In contrast, gut microbiomes may regulate the persistence of certain aspects of systemic autoimmunity.

IL-23 Promotes a Coordinated B Cell Germinal Center Program for Class-Switch Recombination to IgG2b in BXD2 Mice.

IL-23 promotes autoimmune disease, including Th17 CD4 T cell development and autoantibody production. In this study, we show that a deficiency of the p19 component of IL-23 in the autoimmune BXD2 (BXD2-p19-/- ) mouse leads to a shift of the follicular T helper cell program from follicular T helper (Tfh)-IL-17 to Tfh-IFN-γ. Although the germinal center (GC) size and the number of GC B cells remained the same, BXD2-p19-/- mice exhibited a lower class-switch recombination (CSR) in the GC B cells, leading to lower serum levels of IgG2b. Single-cell transcriptomics analysis of GC B cells revealed that whereas Ifngr1, Il21r, and Il4r genes exhibited a synchronized expression pattern with Cxcr5 and plasma cell program genes, Il17ra exhibited a synchronized expression pattern with Cxcr4 and GC program genes. Downregulation of Ighg2b in BXD2-p19-/- GC B cells was associated with decreased expression of CSR-related novel base excision repair genes that were otherwise predominantly expressed by Il17ra + GC B cells in BXD2 mice. Together, these results suggest that although IL-23 is dispensable for GC formation, it is essential to promote a population of Tfh-IL-17 cells. IL-23 acts indirectly on Il17ra + GC B cells to facilitate CSR-related base excision repair genes during the dark zone phase of GC B cell development.

Autoreactive B cells in SLE, villains or innocent bystanders?

The current concepts for development of autoreactive B cells in SLE (systemic lupus erythematosus) focus on extrinsic stimuli and factors that provoke B cells into tolerance loss. Traditionally, major tolerance loss pathways are thought to be regulated by factors outside the B cell including autoantigen engagement of the B-cell receptor (BCR) with simultaneous type I interferon (IFN) produced by dendritic cells, especially plasmacytoid dendritic cells (pDCs). Later, in autoreactive follicles, B-cells encounter T-follicular helper cells (Tfh) that produce interleukin (IL)-21, IL-4 and pathogenic cytokines, IL-17 and IFN gamma (IFNÉ£). This review discusses these mechanisms and also highlights recent advances pointing to the peripheral transitional B-cell stage as a major juncture where transient autocrine IFNß expression by developing B-cells imprints a heightened susceptibility to external factors favoring differentiation into autoantibody-producing plasmablasts. Recent studies highlight transitional B-cell heterogeneity as a determinant of intrinsic resistance or susceptibility to tolerance loss through the shaping of B-cell responsiveness to cytokines and other environment factors.

Dysregulation of T Follicular Helper Cells in Lupus.

Although multiple and overlapping mechanisms are ultimately responsible for the immunopathology observed in patients with systemic lupus erythematosus, autoreactive Abs secreted by autoreactive plasma cells (PCs) are considered to play a critical role in disease progression and immunopathology. Given that PCs derive from the germinal centers (GC), long-term dysregulated GC reactions are often associated with the development of spontaneous autoantibody responses and immunopathology in systemic lupus erythematosus patients. In this review, we summarize the emerging evidence concerning the roles of T follicular helper cells in regulating pathogenic GC and autoreactive PC responses in lupus.

Cutting Edge: Intracellular IFN-ß and Distinct Type I IFN Expression Patterns in Circulating Systemic Lupus Erythematosus B Cells.

In systemic lupus erythematosus (SLE), type I IFNs promote induction of type I IFN-stimulated genes (ISG) and can drive B cells to produce autoantibodies. Little is known about the expression of distinct type I IFNs in lupus, particularly high-affinity IFN-ß. Single-cell analyses of transitional B cells isolated from SLE patients revealed distinct B cell subpopulations, including type I IFN producers, IFN responders, and mixed IFN producer/responder clusters. Anti-Ig plus TLR3 stimulation of SLE B cells induced release of bioactive type I IFNs that could stimulate HEK-Blue cells. Increased levels of IFN-ß were detected in circulating B cells from SLE patients compared with controls and were significantly higher in African American patients with renal disease and in patients with autoantibodies. Together, the results identify type I IFN-producing and -responding subpopulations within the SLE B cell compartment and suggest that some patients may benefit from specific targeting of IFN-ß.

Unmasking Fucosylation: from Cell Adhesion to Immune System Regulation and Diseases.

Fucosylation is a biological process broadly observed in vertebrates, invertebrates, plants, bacteria, and fungi. Fucose moieties on cell-surface glycans are increasingly recognized as critical to many cell-cell interaction and signaling processes. One of the characteristic roles of fucose is its regulation of selectin-dependent leukocyte adhesion that has been well studied over the last two decades. Recent studies of fucose in immune cell development and function regulation have significantly expanded the contemporary understanding of fucosylation. From cellular adhesion to immune regulation, herein we discuss the use of gene knockout studies, competitive inhibitors of fucose-containing glycan, and metabolic inhibitors of fucose biosynthesis to probe fucosylated glycan biosynthesis and signaling and its functional consequences. Promising clinical and preclinical applications in sickle cell disease, rheumatoid arthritis, tumor inhibition, metastasis prevention, antibody-dependent cell-mediated cytotoxicity, chemoresistance reversal, and in improving chemotherapy-related side effects and recovery are reviewed.

Role of production of type I interferons by B cells in the mechanisms and pathogenesis of systemic lupus erythematosus.

Type I interferons (IFNs) have a prominent role in many aspects of normal innate and adaptive immunity and autoimmunity. However, cell-type specific information about type I IFN expression and autocrine/paracrine signaling is sparse and mostly focused on non-lymphocyte and non-immune cell populations. A major function of B cells is cytokine production, but surprisingly, type I IFN production by B cells in systemic lupus erythematosus (SLE) has not been thoroughly investigated. This is due, in part, to the established view that plasmacytoid dendritic cells (pDCs) are the primary source of pathogenic type I IFN in lupus. Recent studies, however, have provided evidence to challenge this paradigm. Here, we discuss data supporting a new concept that the production of type I IFN, especially IFNß, by early stage transitional B cells may be an important source of type I IFN to support autoreactive B cell development in lupus. These findings, if confirmed, may provide a new paradigm in designing and developing more effective therapies for preventing the formation of autoreactive B cells.

Cutting Edge: Endogenous IFN-ß Regulates Survival and Development of Transitional B Cells.

The transitional stage of B cell development is a formative stage in the spleen where autoreactive specificities are censored as B cells gain immune competence, but the intrinsic and extrinsic factors regulating survival of transitional stage 1 (T1) B cells are unknown. We report that B cell expression of IFN-ß is required for optimal survival and TLR7 responses of transitional B cells in the spleen and was overexpressed in T1 B cells from BXD2 lupus-prone mice. Single-cell gene expression analysis of B6 Ifnb+/+ versus B6 Ifnb-/- T1 B cells revealed heterogeneous expression of Ifnb in wild-type B cells and distinct gene expression patterns associated with endogenous IFN-ß. Single-cell analysis of BXD2 T1 B cells revealed that Ifnb is expressed in early T1 B cell development with subsequent upregulation of Tlr7 and Ifna1 Together, these data suggest that T1 B cell expression of IFN-ß plays a key role in regulating responsiveness to external factors.

Interferon-induced mechanosensing defects impede apoptotic cell clearance in lupus.

Systemic lupus erythematosus (SLE) is a severe autoimmune disease that is associated with increased circulating apoptotic cell autoantigens (AC-Ags) as well as increased type I IFN signaling. Here, we describe a pathogenic mechanism in which follicular translocation of marginal zone (MZ) B cells in the spleens of BXD2 lupus mice disrupts marginal zone macrophages (MZMs), which normally clear AC debris and prevent follicular entry of AC-Ags. Phagocytosis of ACs by splenic MZMs required the megakaryoblastic leukemia 1 (MKL1) transcriptional coactivator-mediated mechanosensing pathway, which was maintained by MZ B cells through expression of membrane lymphotoxin-α1ß2 (mLT). Specifically, type I IFN-induced follicular shuttling of mLT-expressing MZ B cells disengaged interactions between these MZ B cells and LTß receptor-expressing MZMs, thereby downregulating MKL1 in MZMs. Loss of MKL1 expression in MZMs led to defective F-actin polymerization, inability to clear ACs, and, eventually, MZM dissipation. Aggregation of plasmacytoid DCs in the splenic perifollicular region, follicular translocation of MZ B cells, and loss of MKL1 and MZMs were also observed in an additional murine lupus model and in the spleens of patients with SLE. Collectively, the results suggest that lupus might be interrupted by strategies that maintain or enhance mechanosensing signaling in the MZM barrier to prevent follicular entry of AC-Ags.

General Approach for Tetramer-Based Identification of Autoantigen-Reactive B Cells: Characterization of La- and snRNP-Reactive B Cells in Autoimmune BXD2 Mice.

Autoreactive B cells are associated with the development of several autoimmune diseases, including systemic lupus erythematosus and rheumatoid arthritis. The low frequency of these cells represents a major barrier to their analysis. Ag tetramers prepared from linear epitopes represent a promising strategy for the identification of small subsets of Ag-reactive immune cells. This is challenging given the requirement for identification and validation of linear epitopes and the complexity of autoantibody responses, including the broad spectrum of autoantibody specificities and the contribution of isotype to pathogenicity. Therefore, we tested a two-tiered peptide microarray approach, coupled with epitope mapping of known autoantigens, to identify and characterize autoepitopes using the BXD2 autoimmune mouse model. Microarray results were verified through comparison with established age-associated profiles of autoantigen specificities and autoantibody class switching in BXD2 and control (C57BL/6) mice and high-throughput ELISA and ELISPOT analyses of synthetic peptides. Tetramers were prepared from two linear peptides derived from two RNA-binding proteins (RBPs): lupus La and 70-kDa U1 small nuclear ribonucleoprotein. Flow cytometric analysis of tetramer-reactive B cell subsets revealed a significantly higher frequency and greater numbers of RBP-reactive marginal zone precursor, transitional T3, and PDL-2(+)CD80(+) memory B cells, with significantly elevated CD69 and CD86 observed in RBP(+) marginal zone precursor B cells in the spleens of BXD2 mice compared with C57BL/6 mice, suggesting a regulatory defect. This study establishes a feasible strategy for the characterization of autoantigen-specific B cell subsets in different models of autoimmunity and, potentially, in humans.

Odanacatib, A Cathepsin K-Specific Inhibitor, Inhibits Inflammation and Bone Loss Caused by Periodontal Diseases.

BACKGROUND: Periodontitis is a bacteria-induced inflammatory disease mainly affecting periodontal tissues, leading to periodontal inflammation, bone breakdown, and loss of the tooth. The main obstacle for treating periodontitis effectively is the difficulty in finding a target that can inhibit bone loss and inflammation simultaneously. Recent studies showed that cathepsin K (CTSK) might have functions in the immune system besides its role in osteoclasts. Thus, targeting CTSK would have a potential therapeutic effect in both the bone system and the immune system during the progression of periodontitis. METHODS: In the current study, a small molecular inhibitor (odanacatib [ODN]) is explored to inhibit the function of CTSK in a bacteria-induced periodontitis mouse model. RESULTS: The application of ODN decreased the number of osteoclasts, macrophages, and T cells, as well as the expression of Toll-like receptors (TLRs) in the periodontitis lesion area. Furthermore, lack of CTSK inhibited the expression of TLR4, TLR5, and TLR9 and their downstream cytokine signaling in the gingival epithelial cells in periodontitis lesions, demonstrating that the innate immune response was inhibited in periodontitis. CONCLUSION: The present results show that inhibition of CTSK can prevent bone loss and the immune response during the progression of periodontitis, indicating that CTSK is a promising target for treating inflammatory diseases such as periodontitis by affecting both osteoclasts and the immune system.

Identification of follicular T helper cells in tissue sections.

Follicular T helper (Tfh) cells are a critical population of CD4 T helper cells that are primarily localized in the germinal centers (GCs) to help B cell maturation and antibody production. Tfh cells can be identified in tissue sections based on the expression of a panel of classical Tfh surface makers, transcription marker(s), and effector-function cytokines, as well as by their unique anatomic proximity to other GC cells, including follicular dendritic cells (FDC) and GC B cells. Here, we describe an immunofluorescence staining method for visualization of GC Tfh cells in frozen spleen tissue sections of the autoimmune BXD2 mouse using a confocal imaging strategy. Tfh cells were characterized based on the expression of CD4, CXCR5, Bcl6, IL-21, and IL-17.

Dysregulated cytokine production by dendritic cells modulates B cell responses in the NZM2410 mouse model of lupus.

The breakdown in tolerance of autoreactive B cells in the lupus-prone NZM2410-derived B6.Sle1.Sle2.Sle3 (TC) mice results in the secretion of autoantibodies. TC dendritic cells (DCs) enhance B cell proliferation and antibody secretion in a cytokine-dependent manner. However, the specific cytokine milieu by which TC DCs activate B cells was not known. In this study, we compared TC and C57BL/6 (B6) control for the distribution of DC subsets and for their production of cytokines affecting B cell responses. We show that TC DCs enhanced B cell proliferation through the production of IL-6 and IFN-γ, while antibody secretion was only dependent on IL-6. Pre-disease TC mice showed an expanded PDCA1(+) cells prior to disease onset that was localized to the marginal zone and further expanded with age. The presence of PDCA1(+) cells in the marginal zone correlated with a Type I Interferon (IFN) signature in marginal zone B cells, and this response was higher in TC than B6 mice. In vivo administration of anti-chromatin immune complexes upregulated IL-6 and IFN-γ production by splenic DCs from TC but not B6 mice. The production of BAFF and APRIL was decreased upon TC DC stimulation both in vitro and in vivo, indicating that these B cell survival factors do not play a role in B cell modulation by TC DCs. Finally, TC B cells were defective at downregulating IL-6 expression in response to anti-inflammatory apoptotic cell exposure. Overall, these results show that the TC autoimmune genetic background induces the production of B cell-modulating inflammatory cytokines by DCs, which are regulated by the microenvironment as well as the interplay between DC.

IL-23 promotes TCR-mediated negative selection of thymocytes through the upregulation of IL-23 receptor and RORγt.

Transient thymic involution is frequently found during inflammation, yet the mode of action of inflammatory cytokines is not well defined. Here we report that interleukin-23 (IL-23) production by the thymic dendritic cells (DCs) promotes apoptosis of the CD4(hi)CD8(hi) double-positive (DP) thymocytes. A deficiency in IL-23 signalling interferes with negative selection in the male D(b)/H-Y T-cell receptor (TCR) transgenic mice. IL-23 plus TCR signalling results in significant upregulation of IL-23 receptor (IL-23R) expressed predominantly on CD4(hi)CD8(hi)CD3(+)αßTCR(+) DP thymocytes, and leads to RORγt-dependent apoptosis. These results extend the action of IL-23 beyond its peripheral effects to a unique role in TCR-mediated negative selection including elimination of natural T regulatory cells in the thymus.