Immunological role of Gas6/TAM signaling in hemostasis and thrombosis.

The immune system is an emerging regulator of hemostasis and thrombosis. The concept of immunothrombosis redefines the relationship between coagulation and immunomodulation, and the Gas6/Tyro3-Axl-MerTK (TAM) signaling pathway builds the bridge across them. During coagulation, Gas6/TAM signaling pathway not only activates platelets, but also promotes thrombosis through endothelial cells and vascular smooth muscle cells involved in inflammatory responses. Thrombosis appears to be a common result of a Gas6/TAM signaling pathway-mediated immune dysregulation. TAM TK and its ligands have been found to be involved in coagulation through the PI3K/AKT or JAK/STAT pathway in various systemic diseases, providing new perspectives in the understanding of immunothrombosis. Gas6/TAM signaling pathway serves as a breakthrough target for novel therapeutic strategies to improve disease management. Many preclinical and clinical studies of TAM receptor inhibitors are in process, confirming the pivotal role of Gas6/TAM signaling pathway in immunothrombosis. Therapeutics targeting the TAM receptor show potential both in anticoagulation management and immunotherapy. Here, we review the immunological functions of the Gas6/TAM signaling pathway in coagulation and its multiple mechanisms in diseases identified to date, and discuss the new clinical strategies that may generated by these roles.

Elevated expression of hsa_circ_0000479 in neutrophils correlates with features of systemic lupus erythematosus.

OBJECTIVE: Accumulating evidence suggests that differentially expressed circular RNAs (circRNAs) play critical roles in immune cells of systemic lupus erythematosus (SLE) patients. Hsa_circ_0000479 has been studied in the field of cancer and infection, whereas seldom studied in autoimmune diseases. The aim of this study was to investigate the role and clinical value of neutrophil hsa_circ_0000479 in SLE. METHODS: The expression levels of hsa_circ_0000479 in both healthy individuals and SLE patients' neutrophils were detected by qPCR and compared with those in peripheral blood mononuclear cells (PBMCs) . In addition, the correlation of hsa_circ_0000479 levels in neutrophils with the clinical and immunological features of SLE patients was also analysed. RESULTS: The expression levels of hsa_circ_0000479 in the patients with SLE were significantly higher in neutrophils than that of PBMCs, and also significantly higher than that in healthy controls (HCs). Moreover, the expression levels of hsa_circ_0000479 in neutrophils were negatively associated with absolute neutrophil count and complement 3 (C3), whereas positively correlated with anti-dsDNA and anti-nucleosome antibodies in SLE. In addition, SLE patients with higher levels of hsa_circ_0000479 demonstrated more several clinical manifestations, including Raynaud's phenomenon, alopecia and leucopenia. CONCLUSIONS: Hsa_circ_0000479 is up-regulated in neutrophils of SLE patients, and is also associated with several important laboratory indicators and clinical manifestations, suggesting that hsa_circ_0000479 in neutrophils was one of probable factors involved in the pathogenesis of SLE with potential clinical value.

Hsa_circ_0000479 was expressed in neutrophils and was considerably higher than that of PBMCs in SLE patients.The neutrophil hsa_circ_0000479 was correlated with laboratory parameters, including NEUT, C3, anti-dsDNA antibodies and AnuA, in addition to being associated with Raynaud's phenomenon, alopecia, and leucopenia in patients with SLE.Hsa_circ_0000479 in neutrophils may play an influential role in SLE patients and will be important to understand the pathogenesis, stratification and treatment in SLE.

Proinflammatory phenotype of B10 and B10pro cells elicited by TNF-α in rheumatoid arthritis.

OBJECTIVES: B10 and B10pro cells suppress immune responses via secreting interleukin (IL)-10. However, their regulators and underlying mechanisms, especially in human autoimmune diseases, are elusive. This study aimed to address these questions in rheumatoid arthritis (RA), one of the most common highly disabling autoimmune diseases. METHODS: The frequencies and functions of B10 and B10pro cells in healthy individuals and patients with RA were first analysed. The effects of proinflammatory cytokines, particularly tumour necrosis factor (TNF)-α on the quantity, stability and pathogenic phenotype of these cells, were then assessed in patients with RA before and after anti-TNF therapy. The underlying mechanisms were further investigated by scRNA-seq database reanalysis, transcriptome sequencing, TNF-α-/- and B cell-specific SHIP-1-/- mouse disease model studies. RESULTS: TNF-α was a key determinant for B10 cells. TNF-α elicited the proinflammatory feature of B10 and B10pro cells by downregulating IL-10, and upregulating interferon-γ and IL-17A. In patients with RA, B10 and B10pro cells were impaired with exacerbated proinflammatory phenotype, while anti-TNF therapy potently restored their frequencies and immunosuppressive functions, consistent with the increased B10 cells in TNF-α-/- mice. Mechanistically, TNF-α diminished B10 and B10pro cells by inhibiting their glycolysis and proliferation. TNF-α also regulated the phosphatidylinositol phosphate signalling of B10 and B10pro cells and dampened the expression of SHIP-1, a dominant phosphatidylinositol phosphatase regulator of these cells. CONCLUSIONS: TNF-α provoked the proinflammatory phenotype of B10 and B10pro cells by disturbing SHIP-1 in RA, contributing to the disease development. Reinstating the immunosuppressive property of B10 and B10pro cells might represent novel therapeutic approaches for RA.

Leukocyte Ig-like receptor A3 facilitates inflammation, migration and invasion of synovial tissue-derived fibroblasts via ERK/JNK activation.

OBJECTIVE: Leukocyte Ig-like receptor A3 (LILRA3) is a soluble receptor belongs to the immunoglobulin superfamily. Our previous studies demonstrated that LILRA3 is a common genetic risk for multiple autoimmune diseases, including RA. Functional LILRA3 conferred increased risk of joint destruction in patients with early RA. We undertook this study to further investigate the pathological role of LILRA3 in joint inflammation of RA. METHODS: Soluble LILRA3 was measured by ELISA. LILRA3 plasmids were transfected into human fibroblast-like synoviocytes (FLSs) using electroporation. Activation of extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) was determined by western blots. Cytokine transcripts were quantified by real-time PCR. Migratory and invasive capacities of FLSs were evaluated using transwell migration and Matrigel invasion assays. FLS apoptosis was analysed using flow cytometry. Colocalization of LILRA3, LILRB1 and HLA-G in RA-FLSs was visualized by immunofluorescence staining. RESULTS: Soluble LILRA3 was specifically expressed in synovial fluid and serum LILRA3 was significantly increased and positively correlated with disease activity/severity in RA patients. LILRA3 induced an increased expression of IL-6, IL-8 and MMP3 in RA-FLSs. In vitro LILRA3 stimulation or overexpression promoted RA-FLS migration and invasion, and enhanced phosphorylation of ERK/JNK. Inhibition of ERK/JNK resulted in suppression of IL-6/IL-8 expression in LILRA3-stimulated RA-FLSs. LILRA3 was co-localized with its homologue LILRB1 and shared ligand HLA-G in RA-FLSs. CONCLUSION: The present study provides the first evidence that soluble LILRA3 is a novel proinflammatory mediator involved in synovial inflammation by promoting RA-FLS activation, migration and invasion, probably through the ERK/JNK signalling pathways.

B cell subsets in adult-onset Still's disease: potential candidates for disease pathogenesis and immunophenotyping.

BACKGROUND: Adult-onset Still's disease (AOSD) is a systemic autoinflammatory disorder of unknown etiology. B cells are critical participants in different rheumatic diseases, and their roles in AOSD are rarely investigated. This study aimed to unveil the B cell subset features in AOSD and provide evidence for B cell-based diagnosis and targeted therapies of AOSD. METHODS: B cell subsets in the peripheral blood of AOSD patients and healthy controls (HCs) were detected by flow cytometry. Firstly, the frequencies of B cell subsets were compared. Then, the correlation analysis was performed to explore the correlation between B cell subsets and clinical manifestations in AOSD. Finally, unbiased hierarchical clustering was performed to divide AOSD patients into three groups with different B cell subset features, and the clinical characteristics of the three groups were compared. RESULTS: The frequencies of B cell subsets were altered in AOSD patients. Disease-promoting subsets (such as naïve B cells, double negative B cells (DN B cells), and plasmablasts) increased, and potential regulatory subsets (such as unswitched memory B cells (UM B cells) and CD24hiCD27+ B cells (B10 cells)) decreased in the peripheral blood of AOSD patients. In addition, the altered B cell subsets in AOSD correlated with the clinical and immunological features, such as immune cells, coagulation features, and liver enzymes. Intriguingly, AOSD patients could be divided into three groups with distinct B cell immunophenotyping: group 1 (naïve B cells-dominant), group 2 (CD27+ memory B cells-dominant), and group 3 (precursors of autoantibody-producing plasma cells-dominant). Moreover, these three group patients demonstrated differential manifestations, including immune cells, liver or myocardial enzymes, coagulation features, and systemic score. CONCLUSIONS: B cell subsets are significantly altered in AOSD patients, potentially contributing to the disease pathogenesis. These findings would inspire B cell-based diagnosis and targeted therapies for this refractory disease.

Decreased perforin-producing B cells correlate with systemic lupus erythematosus.

OBJECTIVES: It has been proved that B cells play indispensable roles in immunity via producing cytokines and secreting antibodies. Aberrant B cells are considered as the major participants in the pathogenesis of systemic lupus erythematosus (SLE). Recently, perforin (PFP)-producing B cell has been identified, serving as a new type of potential anti-tumour effector cells. However, the roles and characteristics of the PFP-producing B cells in SLE remain unclear. METHODS: The frequencies of PFP-producing B cells in peripheral blood of heathy controls (HC) and SLE patients were detected by flow cytometry, and their correlation with the patient clinical and immunological features were analysed. The capacities of these cells in producing PFP were also compared between HC and SLE by RT-qPCR and ELISpot analyses. RESULTS: In this study, we demonstrated that B cells could produce PFP and was further enhanced upon anti-BCR and IL-21 stimulation. In patients with SLE, the frequencies of these PFP-producing B cells were decreased and negatively correlated with the clinical characteristics. Further analysis revealed that SLE patients with vasculitis and pleurisy showed even lower frequencies of PFP-producing B cells. CONCLUSIONS: These findings revealed that B cells could produce PFP, and a decrease in these cells was associated with SLE pathogenesis.

Tonsillar Microbiome-Derived Lantibiotics Induce Structural Changes of IL-6 and IL-21 Receptors and Modulate Host Immunity.

Emerging evidence emphasizes the functional impacts of host microbiome on the etiopathogenesis of autoimmune diseases, including rheumatoid arthritis (RA). However, there are limited mechanistic insights into the contribution of microbial biomolecules especially microbial peptides toward modulating immune homeostasis. Here, by mining the metagenomics data of tonsillar microbiome, a deficiency of the encoding genes of lantibiotic peptides salivaricins in RA patients is identified, which shows strong correlation with circulating immune cells. Evidence is provided that the salivaricins exert immunomodulatory effects in inhibiting T follicular helper (Tfh) cell differentiation and interleukin-21 (IL-21) production. Mechanically, salivaricins directly bind to and induce conformational changes of IL-6 and IL-21 receptors, thereby inhibiting the bindings of IL-6 and IL-21 to their receptors and suppressing the downstream signaling pathway. Finally, salivaricin administration exerts both prophylactic and therapeutic effects against experimental arthritis in a murine model of RA. Together, these results provide a mechanism link of microbial peptides-mediated immunomodulation.

Scavenger receptor A in immunity and autoimmune diseases: Compelling evidence for targeted therapy.

INTRODUCTION: Scavenger receptor A (SR-A) is reported to be involved in innate and adaptive immunity and in recent years, the soluble form of SR-A has also been identified. Intriguingly, SR-A displays double-edged sword features in different diseases. Moreover, targeted therapy on SR-A, including genetic modulation, small molecule inhibitor, inhibitory peptides, fucoidan, and blocking antibodies, provides potential strategies for treatment. Currently, therapeutics targeting SR-A are in preclinical studies and clinical trials, revealing great perspectives in future immunotherapy. AREAS COVERED: Through searching PubMed (January 1979-March 2022) and clinicaltrials.gov, we review most of the research and clinical trials involving SR-A. This review briefly summarizes recent study advances on SR-A, with particular concern on its role in immunity and autoimmune diseases. EXPERT OPINION: Given the emerging evidence of SR-A in immunity, its targeted therapy has been studied in various diseases, especially autoimmune diseases. However, many challenges still remain to be overcome, such as the double-sworded effects and the specific isoform targeting. For further clinical success of SR-A targeted therapy, the crystal structure illustration and the dual function discrimination of SR-A should be further investigated. Nevertheless, although challenging, targeting SR-A would be a potential effective strategy in the treatment of autoimmune diseases and other immune-related diseases.

SR-A neutralizing antibody: potential drug candidate for ameliorating osteoclastogenesis in rheumatoid arthritis.

Rheumatoid arthritis (RA) is an autoimmune disease characterized by proliferative synovitis with deterioration of cartilage and bone. Osteoclasts (OCs) are the active participants in the bone destruction of RA. Although with great advances, most current therapeutic strategies for RA have limited effects on bone destruction. Macrophage scavenger receptor A (SR-A) is a class of pattern recognition receptors (PRRs) involved in bone metabolism and OC differentiation. More recently, our study revealed the critical role of SR-A in RA diagnosis and pathogenesis. Here, we further demonstrated that serum SR-A levels were positively correlated with bone destruction in patients with RA. Anti-SR-A neutralizing antibodies significantly inhibited OC differentiation and bone absorption in vitro in patients with RA, but not in healthy individuals, dampening the expression of OC-specific genes such as tartrate-resistant acid phosphatase (TRAP), cathepsin K (CTSK), and matrix metalloproteinase-9 (MMP-9). Similar results were also seen in collagen-induced arthritis (CIA) mice in vitro. Moreover, the anti-SR-A neutralizing antibody could further ameliorate osteoclastogenesis in vivo and ex vivo in CIA mice, accompanied by decreased serum levels of C-terminal telopeptide and IL-6, exhibiting potential protective effects. These results suggest that blockade of SR-A using anti-SR-A neutralizing antibodies might provide a promising therapeutic strategy for bone destruction in the RA.

Dysfunction of CD27+IgD+ B cells correlates with aggravated systemic lupus erythematosus.

OBJECTIVE: The apoptotic signaling pathway is obviously disordered in systemic lupus erythematosus (SLE). Natural IgM (nIgM) is important in clearing apoptotic cells and preventing them from triggering deleterious autoimmunity. B-1 and innate-like B (ILBs) cells are the main nIgM producers. Human CD27+IgD+ B cells (un-switched memory B cells) are considered ILBs. However, their functional properties in SLE remain undefined. METHODS: Peripheral blood sample of 50 SLE patients and 50 healthy controls were collected, and twelve SLE patients were assessed in a follow-up study. The amount of CD27+IgD+ B cell in each population was analyzed by flow cytometry. The IgM and IL-10 levels of CD27+IgD+ B cell were assessed by ELISPOT and qRT-PCR, respectively. SPSS 17.0 (SPSS, USA) was employed for data analysis. P < 0.05 indicated statistical significance. RESULT: The amounts of CD27+IgD+ B cell were significantly decreased in SLE patients than healthy control (P < 0.01). CD27+IgD+ B cell amounts were positively correlated with WBC (r = 0.337, P = 0.017), platelet count (r = 0.396, P = 0.004), and serum C3 levels (r = 0.415, P = 0.003) and negatively correlated with serum creatinine levels (r = - 0.285, P = 0.045), SLEDAI(r = - 0.724, P = 0.000), and anti-dsDNA(r = - 0.477, P = 0.000). The IgM and IL-10 levels of CD27+IgD+ B in active SLE were decreased than healthy control (P < 0.001). Moreover, CD27+IgD+ B cells are increased in SLE cases after treatment than before treatment (P < 0.001). CONCLUSION: The amounts of CD27+IgD+ B cell were significantly decreased in SLE patients compared with the healthy population, and CD27+IgD+ B cell was verified to be correlated with clinical and immunological features in SLE patients. CD27+IgD+ B cells had impaired function associated with IgM and IL-10 production in active SLE. Moreover, the amounts of CD27+IgD+ B cells were recovered to the normal level in SLE cases with treatment-related disease remission. Key Points • CD27+IgD+ B cell amounts are significantly decreased in SLE patients than healthy control. • CD27+IgD+ B cells are functionally impaired in producing natural antibody-like IgM and IL-10 in SLE patients. • CD27+IgD+ B cell amounts are correlated with clinical and immunological features in SLE.

Double-negative (DN) B cells: an under-recognized effector memory B cell subset in autoimmunity.

Human B cells could be divided into four classical subsets based on CD27 and immunoglobulin (Ig)D expression. Distinct from the other three well-studied subsets, CD27- IgD- B cells, also termed as double-negative (DN) B cells, have long been neglected. However, in recent years emerging evidence shows that DN B cells are unique memory B cells with important functions. They are expanded in a variety of diseases, especially in autoimmune diseases, contributing to the disease pathogenesis. Here, we briefly review the studies on DN B cells, including their origins, characteristics, subsets and roles in diseases, to try to bring new insights into this under-recognized B cell subset.

LAG3 (CD223) and autoimmunity: Emerging evidence.

Immune checkpoint molecules play pivotal roles in maintaining the immune homeostasis. Targeting these molecules, such as the classical Cytotoxic T-Lymphocyte Antigen 4 (CTLA4) and Programmed Cell Death Protein 1 (PD1), achieves great success in treating cancers. However, not all the patients respond well. This urges the immunologists to identify novel immune checkpoint molecules. Lymphocyte activation gene-3 (LAG3; CD223) is a newly identified inhibitory receptor. It is expressed on a variety of immune cells, including CD4+ T cells, CD8+ T cells, Tregs, B cells, and NK cells. Its unique intracellular domains, signaling patterns as well as the striking synergy observed in its targeted therapy with anti-PD1 indicate the important role of LAG3 in maintaining immune tolerance. Currently, a variety of agents targeting LAG3 are in clinical trials, revealing great perspectives in the future immunotherapy. In this review, we briefly summarize the studies on LAG3, including its structure, isoforms, ligands, signaling, function, roles in multiple diseases, as well as the latest targeted therapeutic advances, with particular concern on the potential association of LAG3 with autoimmune diseases.

CD70-mediated CD27 expression downregulation contributed to the regulatory B10 cell impairment in rheumatoid arthritis.

Regulatory B10 cells have been shown to exhibit impaired functions in autoimmune diseases. However, the underlying mechanism is still obscure. In the present study, we aimed to understand the regulatory characteristics of regulatory B10 cells and how these cells are involved in the development of rheumatoid arthritis (RA). Here, we chose CD19+CD24hiCD27+ as the phenotype of regulatory B10 cells. We found that the frequencies of CD19+CD24hiCD27+ regulatory B10 cells were decreased and that their IL-10-producing function was impaired in patients with RA compared with healthy controls (HCs). The impairment in CD19+CD24hiCD27+ B10 cells was partially attributed to the decreased expression of CD27 induced by the upregulated CD70 expression on CD19 + B cells and CD4 + T cells. The proportion of CD19+CD24hiCD27+ regulatory B10 cells could be restored by blocking the CD70-CD27 interaction with an anti-CD70 antibody. Furthermore, the CD70-CD27 interaction significantly elevated IL-10 expression and might compensate for the decreased number of CD19+CD24hiCD27+ B cells. Hence, the CD70-CD27 interaction might play a critical role in the numerical and functional impairments of regulatory B10 cells, thus contributing to RA pathogenesis. In conclusion, the change in CD19+CD24hiCD27+ regulatory B10 cells in RA was only a consequence, not the cause, of RA development, but the increased expression of CD70 might be the culprit.

Secreted Protein Acidic and Rich in Cysteine Mediated Biomimetic Delivery of Methotrexate by Albumin-Based Nanomedicines for Rheumatoid Arthritis Therapy.

Rheumatoid arthritis (RA) is one of the most common chronic autoimmune diseases. Despite considerable advances in clinical treatment of RA, suboptimal response to therapy and treatment discontinuation are still unresolved challenges due to systemic toxicity. It is of crucial importance to actively target and deliver therapeutic agents to inflamed joints in order to promote in situ activity and decrease systemic toxicity. In this study, we found that SPARC (secreted protein acidic and rich in cysteine) was overexpressed in the synovial fluid and synovium of RA patients as well as mice with collagen-induced arthritis (CIA), which has been scarcely reported. Building upon the SPARC signature of RA joint microenvironment and the intrinsic high affinity of SPARC for albumin, we fabricated methotrexate-loaded human serum albumin nanomedicines (MTX@HSA NMs) and explored them as biomimetic drug delivery systems for RA therapy. Upon intravenous injection of chlorin e6-labeled MTX@HSA NMs into CIA mice, the fluorescence/magnetic resonance dual-modal imaging revealed higher accumulations and longer retention of MTX@HSA NMs in inflamed joints with respect to free MTX molecules. In vivo therapeutic evaluations suggested that the MTX@HSA NMs were able to attenuate the progression of RA with better efficacy and fewer side effects even at half  dose of administrated MTX in comparison with free MTX. By unraveling the mechanism driving the efficient accumulation of MTX@HSA NMs in RA joints and showing their ability to improve the safety and therapeutic efficacy of MTX, our work sheds light on the development of innovative anti-RA nanomedicines with a strong potential for clinical translation.

Impaired CD27+IgD+ B Cells With Altered Gene Signature in Rheumatoid Arthritis.

Natural antibodies, particularly natural IgM, are proved to play indispensable roles in the immune defenses against common infections. More recently, the protective roles of these natural IgM were also recognized in autoimmune diseases. They are mainly produced by B-1 and innate-like B cells (ILBs). Human CD19+CD27+IgD+ B cells, also termed as un-switched memory B cells, were proposed to be a kind of ILBs. However, functional features and characteristics of these cells in rheumatoid arthritis (RA) remained poorly understood. In this study, we found that human CD27+IgD+ B cells could produce natural antibody-like IgM. Under RA circumstance, the frequencies of these cells were significantly decreased. Moreover, the IgM-producing capacities of these cells were also dampened. Interestingly, the BCR repertoire of these cells was altered in RA, demonstrating decreased diversity with preferential usage alteration from VH3-23D to VH1-8. Single cell sequencing further revealed the proinflammatory biased features of these cells in RA. These CD27+IgD+ B cells were negatively correlated with RA patient disease activities and clinical manifestations. After effective therapy with disease remission in RA, these cells could be recovered. Taken together, these results have revealed that CD27+IgD+ B cells were impaired in RA with dysfunctional features, which might contribute to the disease perpetuation.

Plasma exchange successfully treated macrophage activation syndrome in rheumatoid factor-positive polyarticular juvenile idiopathic arthritis with co-existing pneumonia.

Macrophage activation syndrome (MAS) is one of the serious complications associated with rheumatic diseases, especially systemic juvenile idiopathic arthritis (sJIA). Here we describe a 9-year-old girl with rheumatoid factor (RF)-positive polyarticular JIA, not sJIA, combined with pneumonia who was successfully treated by plasma exchange. She was diagnosed with RF-positive polyarticular JIA based on positive RF and multiple joint swelling and tenderness 3 years ago. She was admitted in our hospital with myalgia for 2 days and a high fever for half a day. Physical examination revealed relapsing joints symptoms and rough breathing sounds of lungs. The laboratory examination showed increased liver enzymes, elevated serum ferritin and procalcitonin (PCT), decreased percentage of nature killer (NK) cells and fibrinogen, and activated macrophage phagocytosing hematopoietic elements in bone marrow. The elevated PCT and chest computed tomography scan confirmed she also had pneumonia. Intravenous methylprednisolone and oral cyclosporine A followed by intravenous immunoglobulin were added on the basis of antibiotics therapy, but clinical symptoms and laboratory findings did not improve. Finally, we changed to plasma exchange once every other day for a total of three times. Within 1 week, the girl recovered from the MAS completely.

Leptin-induced migration and angiogenesis in rheumatoid arthritis is mediated by reactive oxygen species.

Rheumatoid arthritis (RA) is a progressive autoimmune disease affecting the joints. In this study, we investigated the role of the pro-angiogenic factor leptin in regulating reactive oxygen species (ROS) to promote cell migration and angiogenesis in RA. We showed that leptin triggered RA fibroblast-like synoviocyte (FLS) migration by increased ROS expression. Additionally, leptin enhanced human umbilical vein endothelial cell (HUVEC) tube formation in a ROS/hypoxia-inducible factor-1α-dependent manner, accompanied by increased production of vascular endothelial growth factor and interleukin (IL)-6. We also revealed that antagonists of tumor necrosis factor, IL-6 and IL-1ß down-regulated ROS production of RA FLS induced by leptin, which subsequently attenuated RA FLS migration and HUVEC tube formation. These findings demonstrated that leptin might play an important role in RA FLS migration and HUVEC angiogenesis.

SHIP-1 Deficiency in AID+ B Cells Leads to the Impaired Function of B10 Cells with Spontaneous Autoimmunity.

Unlike conventional B cells, regulatory B cells exhibit immunosuppressive functions to downregulate inflammation via IL-10 production. However, the molecular mechanism regulating the production of IL-10 is not fully understood. In this study, we report the finding that activation-induced cytidine deaminase (AID) is highly upregulated in the IL-10-competent B cell (B10) cell from Innp5dfl/flAicdaCre/+ mice, whereas the 5' inositol phosphatase SHIP-1 is downregulated. Notably, SHIP-1 deficiency in AID+ B cells leads to a reduction in cell count and impaired IL-10 production by B10 cells. Furthermore, the Innp5dfl/flAicdaCre/+ mouse model shows B cell-dependent autoimmune lupus-like phenotypes, such as elevated IgG serum Abs, formation of spontaneous germinal centers, production of anti-dsDNA and anti-nuclear Abs, and the obvious deposition of IgG immune complexes in the kidney with age. We observe that these lupus-like phenotypes can be reversed by the adoptive transfer of B10 cells from control Innp5dfl/fl mice, but not from the Innp5dfl/flAicdaCre/+ mice. This finding highlights the importance of defective B10 cells in Innp5dfl/flAicdaCre/+ mice. Whereas p-Akt is significantly upregulated, MAPK and AP-1 activation is impaired in B10 cells from Innp5dfl/flAicdaCre/+ mice, resulting in the reduced production of IL-10. These results show that SHIP-1 is required for the maintenance of B10 cells and production of IL-10, and collectively suggests that SHIP-1 could be a new potential therapeutic target for the treatment of autoimmune diseases.

Impairment of Granzyme B-Producing Regulatory B Cells Correlates with Exacerbated Rheumatoid Arthritis.

Hyperactivated B cells have been demonstrated the contribution to the development of rheumatoid arthritis (RA). While the recognition of the negative regulatory function of B cells further promoted our understanding of their pathogenic role in RA. Recently, a new population of granzyme B (GrB)-producing B cells was identified, which was proved to be involved in cancer and infectious diseases. However, their characteristics and roles in RA remain to be elucidated. In the present study, we aim to further characterize whether B cells could produce GrB and reveal their potential role in the pathogenesis of RA. Here, we further demonstrated peripheral blood B cells from healthy individuals could produce and secrete GrB, which could be enhanced by IL-21 and/or anti-B-cell receptor stimulation. These cells could negatively regulate Th1 and Th17 cells partly via downregulating TCR zeta chain and inducing T cell apoptosis, which might be termed as GrB-producing regulatory B cells (Bregs). These GrB-producing Bregs were significantly decreased under RA circumstance concomitant of lower levels of IL-21 receptor, with impaired regulatory functions on Th1 and Th17 cells. Moreover, the frequencies of these cells were negatively correlated with RA patient disease activity and clinical features. After effective therapy with disease remission in RA, these GrB-producing Bregs could be recovered. Therefore, our data revealed that B cells could produce GrB with immunosuppressive functions, and the impairment of this Breg subset was correlated with RA pathogenesis.

Pathogenic conversion of regulatory B10 cells into osteoclast-priming cells in rheumatoid arthritis.

Regulatory B10 cells were functionally impaired in rheumatoid arthritis (RA), yet the mechanisms were unclear. B cells are recently recognized as important participants in osteoclastogenesis by producing RANKL. In this study, we investigated whether regulatory B10 cells could convert into RANKL-producing cells, thus impairing their immunosuppressive functions in RA and exacerbating the disease progression. Our results showed that human regulatory B10 cells could ectopically express RANKL. Under RA circumstance, RANKL-producing B10 cells expanded dramatically, partially induced by TNF-α. The frequencies of these cells were positively correlated with RA patient disease activities and tender joint counts, but negatively correlated with the frequencies of regulatory B10 cells. Strikingly, RANKL-producing B10 cells from RA patients, but not healthy individuals significantly promoted osteoclast differentiation and bone erosion in a paracrine and cell-cell contact-dependent manner. Moreover, these pathogenic RANKL-producing B10 cells declined while regulatory IL-10-producing B10 cells increased in RA patients with disease remission after therapy. Collectively, these results showed that in RA, regulatory B10 cells demonstrated the potential of converting into RANKL-producing cells, thus exacerbating osteoclast formation, bone destruction and disease progression. Modulating the status of B10 cells might provide novel therapeutic strategies for RA.