Fas (CD95)-transduced signal preferentially stimulates lupus peripheral T lymphocytes

Fas (CD95) is a cell surface receptor whose biological function in circulating peripheral T cells is not well understood. To address the question of abnormal T cell sensitivity to Fas stimulation in systemic lupus erythematosus (SLE), we studied Fas-transduced stimulation and apoptosis in peripheral blood T cells from patients with SLE and normal control. Immobilized anti-Fas monoclonal antibodies (mAb) (imCH-11; IgM type) significantly stimulated SLE T cell proliferation compared to T cells from normal donors and patients with rheumatoid arthritis ( p < 0.003 and p < 0.005, respectively). The soluble form of CH-11 and other immobilized anti-Fas mAb (UB-2, ZB-4; IgG type) failed to stimulate lupus T cells while immobilized human Fas ligand did. Furthermore, imCH-11 induced IL-2 and IL-6 mRNA expression. However, imCH-11 activation failed to induce expression of the T cell activation surface molecules CD25 and CD69. Addition of exogenous ceramide, a second messenger for Fas-mediated apoptosis signaling, also induced T cell proliferation in SLE and normal controls. Moreover, fumonisin B1, a specific ceramide synthase inhibitor, and caspase inhibitors markedly suppressed imCH-11 induced T cell proliferation, suggesting that the ceramide pathway may be involved in Fas-transduced stimulation signals in SLE T cells. These results show that SLE T cells have an alteration in the Fas signal transduction pathway leading to cell proliferation. This defect may be important in Fas-mediated peripheral immune homeostasis.     

Interleukin (IL)‐39 [IL‐23p19/Epstein–Barr virus‐induced 3 (Ebi3)] induces differentiation/expansion of neutrophils in lupus‐prone mice

Interleukin (IL)‐12 family cytokines play critical roles in autoimmune diseases. Our previous study has shown that IL‐23p19 and Epstein–Barr virus‐induced 3 (Ebi3) form a new IL‐12 family heterodimer, IL‐23p19/Ebi3, termed IL‐39, and knock‐down of p19 or Ebi3 reduced diseases by transferred GL7⁺ B cells in lupus‐prone mice. In the present study, we explore further the possible effect of IL‐39 on murine lupus. We found that IL‐39 in vitro and in vivo induces differentiation and/or expansion of neutrophils. GL7⁺ B cells up‐regulated neutrophils by secreting IL‐39, whereas IL‐39‐deficient GL7⁺ B cells lost the capacity to up‐regulate neutrophils in lupus‐prone mice and homozygous CD19^cre (CD19‐deficient) mice. Finally, we found that IL‐39‐induced neutrophils had a positive feedback on IL‐39 expression in activated B cells by secreting B cell activation factor (BAFF). Taken together, our results suggest that IL‐39 induces differentiation and/or expansion of neutrophils in lupus‐prone mice.     

Effect of oestrogen on T cell apoptosis in patients with systemic lupus erythematosus

Defective control of T cell apoptosis is considered to be one of the pathogenetic mechanisms in systemic lupus erythematosus (SLE). Oestrogen has been known to predispose women to SLE and also to exacerbate activity of SLE; however, the role of oestrogen in the apoptosis of SLE T cells has not yet been documented. In this study, we investigated the direct effect of oestrogen on the activation‐induced cell death of T cells in SLE patients. The results demonstrated that oestradiol decreased the apoptosis of SLE T cells stimulated with phorbol 12‐myristate 13‐acetate (PMA) plus ionomycin in a dose‐dependent manner. In addition, oestradiol down‐regulated the expression of Fas ligand (FasL) in activated SLE T cells at the both protein and mRNA levels. In contrast, testosterone increased FasL expression dose‐dependently in SLE T cells stimulated with PMA plus ionomycin. The inhibitory effect of oestradiol on FasL expression was mediated through binding to its receptor, as co‐treatment of tamoxifen, an oestrogen receptor inhibitor, completely nullified the oestradiol‐induced decrease in FasL mRNA expression. Moreover, pre‐treatment of FasL‐transfected L5178Y cells with either oestradiol or anti‐FasL antibody inhibited significantly the apoptosis of Fas‐sensitive Hela cells when two types of cells were co‐cultured. These data suggest that oestrogen inhibits activation‐induced apoptosis of SLE T cells by down‐regulating the expression of FasL. Oestrogen inhibition of T cell apoptosis may allow for the persistence of autoreactive T cells, thereby exhibiting the detrimental action of oestrogen on SLE activity.     

Production of IgG autoantibody requires expression of activation‐induced deaminase in early‐developing B cells in a mouse model of SLE

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by the presence of pathogenic IgG antinuclear antibodies. Pathogenic IgG autoantibody production requires B‐cell activation, leading to the production of activation‐induced deaminase (AID) and class switching of IgM genes to IgG. To understand how and when B cells are activated to produce these IgG autoantibodies, we studied cells from 564Igi, a mouse model of SLE. 564Igi mice develop a disease profile closely resembling that found in human SLE patients, including the presence of IgG antinucleic acid Abs. We have generated 564Igi mice that conditionally express an activation‐induced cytidine deaminase transgene (Aicda^tg), either in all B cells or only in mature B cells. Here, we show that class‐switched pathogenic IgG autoantibodies were produced only in 564Igi mice in which AID was functional in early‐developing B cells, resulting in loss of tolerance. Furthermore, we show that the absence of AID in early‐developing B cells also results in increased production of self‐reactive IgM, indicating that AID, through somatic hypermutation, contributes to tolerance. Our results suggest that the pathophysiology of clinical SLE might also be dependent on AID expression in early‐developing B cells.     

Selenium supplementation suppresses immunological and serological features of lupus in B6.Sle1b mice

Systemic lupus erythematosus (SLE) is a debilitating multi-factorial immunological disorder characterized by increased inflammation and development of anti-nuclear autoantibodies. Selenium (Se) is an essential trace element with beneficial anti-cancer and anti-inflammatory immunological functions. In our previous proteomics study, analysis of Se-responsive markers in the circulation of Se-supplemented healthy men showed a significant increase in complement proteins. Additionally, Se supplementation prolonged the life span of lupus prone NZB/NZW-F1 mice. To better understand the protective immunological role of Se in SLE pathogenesis, we have investigated the impact of Se on B cells and macrophages using in vitro Se supplementation assays and the B6.Sle1b mouse model of lupus with an oral Se or placebo supplementation regimen. Analysis of Se-treated B6.Sle1b mice showed reduced splenomegaly and splenic cellularity compared to untreated B6. Sle1b mice. A significant reduction in total B cells and notably germinal center (GC) B cell numbers was observed. However, other cell types including T cells, Tregs, DCs and pDCs were unaffected. Consistent with reduced GC B cells there was a significant reduction in autoantibodies to dsDNA and SmRNP of the IgG2b and IgG2c subclass upon Se supplementation. We found that increased Se availability leads to impaired differentiation and maturation of macrophages from mouse bone marrow derived progenitors in vitro. Additionally, Se treatment during in vitro activation of B cells with anti-CD40L and LPS inhibited optimal B cell activation. Overall our data indicate that Se supplementation inhibits activation, differentiation and maturation of B cells and macrophages. Its specific inhibitory effect on B cell activation and GC B cell differentiation could be explored as a potential therapeutic supplement for SLE patients.     

Lack of SIGIRR/TIR8 aggravates hydrocarbon oil‐induced lupus nephritis

Multiple genetic factors contribute to the clinical variability of spontaneous systemic lupus erythematosus (SLE) but their role in drug‐induced SLE remain largely unknown. Hydrocarbon oil‐induced SLE depends on mesothelial cell apoptosis and Toll‐like receptor (TLR)‐7‐mediated induction of type I interferons. Hence, we hypothesized that TIR8/SIGIRR, an endogenous TLR inhibitor, prevents oil‐induced SLE. Sigirr‐deficient dendritic cells expressed higher TLR7 mRNA levels and TLR7 activation resulted in increased IL‐12 production in vitro. In vivo, lack of SIGIRR increased surface CD40 expression on spleen CD11c⁺ dendritic cells and MX‐1, TNF, IL‐12, BAFF and BCL‐2 mRNA expression 6 months after pristane injection. Spleen cell counts of CD4^?/CD8^? ‘autoreactive’ T cells and B220⁺ B cells were also increased in Sigirr^?/? mice. Serum autoantibody analysis revealed that Sigirr deficiency specifically enhanced the production of rheumatoid factor (from 4 months of age) and anti‐snRNP IgG (from 5 months of age), while anti‐Smith IgG or anti‐dsDNA IgG were independent of the Sigirr genotype. This effect was sufficient to significantly aggravate lupus nephritis in Sigirr‐deficient mice. Structure model prediction identified the BB loop of SIGIRR's intracellular TIR domain to interact with TLR7 and MyD88. BB loop deletion was sufficient to completely abrogate SIGIRR's inhibitory effect on TLR7 signalling. Thus, TIR8/SIGIRR protects from hydrocarbon oil‐induced lupus by suppressing the TLR7‐mediated activation of dendritic cells, via its intracellular BB loop. Copyright © 2009 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.     

TACI‐dependent APRIL signaling maintains autoreactive B cells in a mouse model of systemic lupus erythematosus

Autoantibodies contribute to the development of systemic lupus erythematosus (SLE). APRIL (a proliferation‐inducing ligand), a member of the TNF superfamily, regulates plasma‐cell survival and binds to TACI (transmembrane activator CAML interactor) and BCMA (B‐cell maturation antigen). We previously showed that APRIL blockade delayed disease onset in lupus‐prone mice. In order to evaluate the role of APRIL receptors in the development of SLE, APRIL, TACI, BCMA , or double TACI.BCMA null mutations were introduced into the Nba2.Yaa (Y‐linked autoimmune acceleration) spontaneous lupus mouse model. Mortality as a consequence of glomerulonephritis (GN) was reduced in Nba2.APRIL^?/?.Yaa , Nba2.TACI^?/?.Yaa and double‐KO mice compared with Nba2.Yaa mice and correlated with lower levels of circulating antibodies, while splenic populations remained unchanged. In contrast, the appearance of symptoms was accelerated in BCMA‐deficient mice, in which TACI signaling was increased. Finally, lupus‐prone mice deficient for the APRIL‐TACI axis produced less pathogenic antibodies and developed less GN. Disease reduction was attributed to impaired T‐independent type 2 responses when the APRIL‐TACI signaling axis was disrupted. Collectively, our results have identified and confirmed APRIL as a new target involved in B‐cell activation, in the maintenance of plasma cell survival and subsequent increased autoantibody production that sustains lupus development in mice.     

High‐Mobility Group Box 1 Inhibition Alleviates Lupus‐Like Disease in BXSB Mice

High‐mobility group box 1 protein (HMGB1), a ubiquitous nuclear DNA‐binding protein, functions as a potent proinflammatory factor. In this study, we evaluated the effects of HMGB1 inhibition on murine lupus using the lupus‐prone model. We treated male BXSB mice with neutralizing anti‐HMGB1 monoclonal antibody (HMGB1 mAb) from age 16 weeks to 26 weeks. The control group received the same amount of control IgG. Lupus‐prone male BXSB mice treated with HMGB1mAb showed attenuated proteinuria, glomerulonephritis, circulating anti‐dsDNA and immune complex deposition. Levels of serum IL‐1β, IL‐6, IL‐17 and IL‐18 were also significantly decreased by administration of HMGB1mAb in lupus‐prone BXSB mice. HMGB1mAb treatment also decreased the caspase‐1 activity in the kidneys of BXSB mice and reduced the mouse mortality. Our study supports that HMGB1 inhibition alleviates lupus‐like disease in BXSB mice and might be a potential treatment option for human SLE.     

FcgammaRIIB deficiency with Fas mutation is sufficient for the development of systemic autoimmune disease

MRL.Fas(lpr/lpr) mice, a model for systemic lupus erythematosus (SLE) and arthritis in humans, have a Fas mutation that results in spontaneous development of systemic autoimmune diseases and a short life span. Half of them die by 5-6 months of age due to massive progression of systemic autoimmune diseases, such as lupus nephritis. However, C57BL/6 (B6).Fas(lpr/lpr) strain does not develop such disorders within the normal life span, indicating that suppressor gene(s) in B6 mice may control the onset and exacerbation of disease. Here, we show that the gene for a unique inhibitory Fc receptor for IgG (Fc gamma RIIB) is a critical SLE suppressor. Fc gamma RIIB-deficient B6.Fas(lpr/lpr) (B6.IIB(-/-)Fas(lpr/lpr)) mice developed systemic autoimmune diseases, including anti-DNA and anti-type II collagen autoantibodies and cryoglobulin production, immune complex glomerulonephritis and arthritis. They were short-lived, due to enhanced autoantibody production by B cells culminating in fatal lupus nephritis. Thus, Fc gamma RIIB deletion with Fas mutation is sufficient for the development of systemic autoimmunity in B6 mice. The inhibitory signaling cascade via Fc gamma RIIB may be critical for suppressing SLE in humans.     

T cell‐derived IFN‐γ downregulates protective group 2 innate lymphoid cells in murine lupus erythematosus

Innate lymphoid cells (ILCs) are important regulators of the immune response and play a crucial role in the restoration of tissue homeostasis after injury. GATA‐3⁺ IL‐13‐ and IL‐5‐producing group 2 innate lymphoid cells (ILC2s) have been shown to promote tissue repair in barrier organs, but despite extensive research on ILCs in the recent years, their potential role in autoimmune diseases is still incompletely understood. In the present study, we investigate the role of ILC2s in the MRL/MpJ‐Fas^lpr (MRL‐lpr) mouse model for severe organ manifestation of systemic lupus erythematosus (SLE). We show that in these MRL‐lpr mice, progression of lupus nephritis is accompanied with a reduction of ILC2 abundance in the inflamed renal tissue. Proliferation/survival and cytokine production of kidney‐residing ILC2s was suppressed by IFN‐γ and, to a lesser extent, by IL‐27 which were produced by activated T cells and myeloid cells in the nephritic kidney, respectively. Most importantly, restoration of ILC2 numbers by IL‐33‐mediated expansion ameliorated lupus nephritis and prevented mortality in MRL‐lpr mice. In summary, we show here that development of SLE‐like kidney inflammation leads to a downregulation of the renal ILC2 response and identify an ILC2‐expanding therapy as a promising treatment approach for autoimmune diseases.     

Expression of an anti‐RNA autoantibody in a mouse model of SLE increases neutrophil and monocyte numbers as well as IFN‐I expression

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by the presence of antinucleic acid autoantibodies, high levels of circulating type I interferon (IFN‐I), and an IFN‐I‐dependent elevated expression of activating FcγR. Increases in neutrophils and monocytes are often observed in clinical SLE, but how these contribute to autoantibody and IFN‐I production is poorly understood. Here, we analyzed SLE pathogenesis in 564Igi mice, an SLE‐model strain carrying gene‐targeted heavy and light chain antibody genes encoding an anti‐RNA autoantibody in a C57BL/6 background. Similar to human SLE patients, 564Igi mice produce anti‐RNA autoantibodies and expanded neutrophil and monocyte populations. These myeloid cells produced IFN‐I and exhibit increased FcγRIV expression induced via an IFN‐I autocrine loop. A direct effect of IFN‐I on 564Igi BM B cells and neutrophils was supported by their upregulation of “IFN‐I signature genes”. In addition, 564Igi developing B cells showed upregulated TLR7 resulting in IgG2a/2b class switch recombination and autoantibody production. Our results indicate that the production of anti‐RNA autoantibody is sufficient to induce an increase of BM, blood, and spleen IFN‐I‐producing neutrophils, and suggest a mechanism by which autoantibody and IFN‐I contribute to SLE by activating B lymphocytes, neutrophils, and monocyte effector cells in vivo.     

Renal‐infiltrating CD11c+ cells are pathogenic in murine lupus nephritis through promoting CD4+ T cell responses

Lupus nephritis (LN) is a major manifestation of systemic lupus erythematosus (SLE), causing morbidity and mortality in 40–60% of SLE patients. The pathogenic mechanisms of LN are not completely understood. Recent studies have demonstrated the presence of various immune cell populations in lupus nephritic kidneys of both SLE patients and lupus‐prone mice. These cells may play important pathogenic or regulatory roles in situ to promote or sustain LN. Here, using lupus‐prone mouse models, we showed the pathogenic role of a kidney‐infiltrating CD11c⁺ myeloid cell population in LN. These CD11c⁺ cells accumulated in the kidneys of lupus‐prone mice as LN progressed. Surface markers of this population suggest their dendritic cell identity and differentiation from lymphocyte antigen 6 complex (Ly6C)^low mature monocytes. The cytokine/chemokine profile of these renal‐infiltrating CD11c⁺ cells suggests their roles in promoting LN, which was confirmed further in a loss‐of‐function in‐vivo study by using an antibody‐drug conjugate (ADC) strategy targeting CX₃CR1, a chemokine receptor expressed highly on these CD11c⁺ cells. However, CX₃CR1 was dispensable for the homing of CD11c⁺ cells into lupus nephritic kidneys. Finally, we found that these CD11c⁺ cells co‐localized with infiltrating T cells in the kidney. Using an ex‐ vivo co‐culture system, we showed that renal‐infiltrating CD11c⁺ cells promoted the survival, proliferation and interferon‐γ production of renal‐infiltrating CD4⁺ T cells, suggesting a T cell‐dependent mechanism by which these CD11c⁺ cells promote LN. Together, our results identify a pathogenic kidney‐infiltrating CD11c⁺ cell population promoting LN progression, which could be a new therapeutic target for the treatment of LN.     

Tuftsin–phosphorylcholine (TPC) equally effective to methylprednisolone in ameliorating lupus nephritis in a mice model

The role of helminth treatment in autoimmune diseases is growing constantly. Systemic lupus erythematosus (SLE) is a multi‐system autoimmune disease with challenging treatment options. Tuftsin–phosphorylcholine (TPC) is a novel helminth‐based compound that modulates the host immune network. This study was conducted to evaluate the potential value of TPC in ameliorating lupus nephritis in a murine model and specifically to compare the efficacy of TPC to the existing first‐line therapy for SLE: corticosteroids (methylprednisolone). Lupus‐prone NZBxW/F₁mice were treated with TPC (5 µg/mouse), methylprednisolone (MP; 5 mg/body weight) or phosphate‐buffered saline (PBS) (control) three times per week once glomerulonephritis, defined as proteinuria of grade > 100 mg/dl, was established. Levels of anti‐dsDNA autoantibodies were evaluated by enzyme‐linked immunosorbent assay (ELISA), splenic cytokines were measured in vitro and the kidney microscopy was analysed following staining. TPC and MP treatments improved lupus nephritis significantly and prolonged survival in NZBxW/F₁ mice. TPC‐treated mice showed a significantly decreased level of proteinuria (P < 0·001) and anti‐dsDNA antibodies (P < 0·001) compared to PBS‐treated mice. Moreover, TPC and MP inhibited the production of the proinflammatory cytokines interferon IFN‐γ, interleukin IL‐1β and IL‐6 (P < 0·001) and enhanced expression of the anti‐inflammatory cytokine IL‐10 (P < 0·001). Finally, microscopy analysis of the kidneys demonstrated that TPC‐treated mice maintained normal structure equally to MP‐treated mice. These data indicate that the small molecule named TPC hinders lupus development in genetically lupus‐prone mice equally to methylprednisolone in most of the cases. Hence, TCP may be employed as a therapeutic potential for lupus nephritis.     

系统性红斑狼疮患者血清IgG对骨髓造血干/祖细胞抑制和凋亡的研究

目的：观察系统性红斑狼疮（SLE）患者血清IgG类抗体体外造血抑制活性及其与造血细胞过度凋亡的关系.方法：应用甲基纤维素集落培养法、原位末端标记及流式细胞术观察系统性红斑狼疮患者血清IgG在体外抑制正常骨髓造血干/祖细胞的增殖及促进正常CD34＋细胞的凋亡.结果：活动期SLE患者血清IgG体外可明显抑制正常骨髓粒-巨噬系祖细胞（CFU-GM）和红系祖细胞（CFU-E）的增殖.这种IgG可特异吸附于正常CD34＋细胞表面,加速CD34＋细胞凋亡,上调CD34＋细胞Fas抗原表达水平.结论：活动期SLE患者血清IgG在体外可抑制正常骨髓造血干/祖细胞的增殖.机制与其上调CD34＋ Fas抗原表达水平而促进CD34＋细胞凋亡有关.     

Dnase1‐deficient mice spontaneously develop a systemic lupus erythematosus‐like disease

Systemic lupus erythematosus (SLE) is an autoimmune disease that has high morbidity and can result in multi‐organ damage. SLE is characterized by dysregulated activation of T‐ and B‐lymphocytes and the production of autoantibodies directed against nuclear components. The endonuclease deoxyribonuclease 1 (DNase1) is abundant in blood and a subset of SLE patients have mutations in DNASE1. Furthermore, a report showed that Dnase1‐deficient mice develop an SLE‐like disease, but these mice also carry a deletion of the gene adjacent to Dnase1, which encodes the chaperone TRAP1/HSP75. We generated a murine strain deficient in Dnase1 with an intact Trap1 gene to examine if a lack of DNase1 is responsible for the development of a spontaneous SLE‐like disease. We show that the Dnase1‐deficient mice do indeed develop an SLE‐like phenotype with elevated autoantibody production by 9 months and kidney damage by 12 months. Notably, this model recapitulates the female bias seen in human SLE patients since female Dnase1‐deficient mice produced the highest concentrations of autoantibodies and had more severe kidney damage than males. Since there is currently no cure for SLE the protective role of DNase1 as demonstrated in our study remains of great therapeutic interest.     

Treatment of lupus in NZB/W F1 mice with monoclonal antibody against Fas ligand

Since Fas ligand (FasL) can induce apoptosis of Fas-bearing cells, Fas/FasL interactions can play a critical role in maintaining self-tolerance. Fas/FasL interactions in lupus-like autoimmune disease have been well characterized in studies using either Fas or FasL mutant mice. However, the effect of the defective FasL-mediated signaling on the establishment of lupus in other mouse strains, such as NZB/W (B/W) F1, remains uncertain. In the present study, we examined the effect of anti-FasL monoclonal antibody (mAb) on the development of lupus. Treatment of B/W F1 mice with anti-FasL mAb augmented IgG1- and IgG2a-type anti-dsDNA Ab production. However, treatment of B/W F1 mice with anti-FasL mAb also significantly prevented the development of lupus nephritis. These results indicate that Fas/FasL interactions not only regulate IgG-type autoantibody production, but also influence the development of lupus nephritis in B/W F1 mice.     

The scaffold protein JLP plays a key role in regulating ultraviolet B‐induced apoptosis in mice

The ultraviolet B (UVB) component of sunlight can cause severe damage to skin cells and even induce skin cancer. Growing evidence indicates that the UVB‐induced signaling network is complex and involves diverse cellular processes. In this study, we investigated the role of c‐Jun NH₂‐terminal kinase‐associated leucine zipper protein (JLP), a scaffold protein for mitogen‐activated protein kinase (MAPK) signaling cascades, in UVB‐induced apoptosis. We found that UVB‐induced skin epidermal apoptosis was prevented in Jlp knockout (KO) as well as in keratinocyte‐specific Jlp KO mice. Analysis of the repair of UVB‐induced DNA damage over time showed no evidence for the involvement of JLP in this process. In contrast, UVB‐stimulated p38 MAPK activation in the skin was impaired in both Jlp KO and keratinocyte‐specific Jlp KO mice. Moreover, topical treatment of UVB‐irradiated mouse skin with a p38 inhibitor significantly suppressed the epidermal apoptosis in wild‐type mice, but not in Jlp KO mice. Our findings suggest that JLP in skin basal keratinocytes plays an important role in UVB‐induced apoptosis by modulating p38 MAPK signaling pathways. This is the first study to show a critical role for JLP in an in vivo response to environmental stimulation.     

Lack of T cells in Act1-deficient mice results in elevated IgM-specific autoantibodies but reduced lupus-like disease

Act1 is a negative regulator of B‐cell activation factor of the TNF family (BAFF) and CD40L‐induced signaling. BALB/C mice lacking Act1 develop systemic autoimmunity resembling systemic lupus erythematosus (SLE) and Sjögren's syndrome (SjS). SLE and SjS are characterized by anti‐nuclear IgG autoantibody (ANA‐IgG) production and inflammation of peripheral tissues. As autoantibody production can occur in a T‐cell dependent or T‐cell independent manner, we investigated the role of T‐cell help during Act1‐mediated autoimmunity. Act1‐deficiency was bred onto C57Bl/6 (B6.Act1^?/?) mice and B6.TCRβ^?/?TCRδ^?/?Act1^?/? (TKO) mice were generated. While TCRβ/δ‐sufficient B6.Act1^?/? mice developed splenomegaly and lymphadenopathy, hypergammaglobulinemia, elevated levels of ANA‐IgG, and kidney pathology, TKO mice failed to develop any such signs of disease. Neither B6.Act1^?/? nor TKO mice developed SjS‐like disease, suggesting that epigenetic interactions on the BALB/C background are responsible for this phenotype in BALB/C.Act1^?/? mice. Interestingly, BAFF‐driven transitional B‐cell abnormalities, previously reported in BALB/C.Act1^?/? mice, were intact in B6.Act1^?/? mice and largely independent of T cells. In conclusion, T cells are necessary for the development of SLE‐like disease in B6.Act1^?/? mice, but not BAFF‐driven transitional B‐cell differentiation.     

Phenotype conversion from rheumatoid arthritis to systemic lupus erythematosus by introduction of Yaa mutation into FcγRIIB‐deficient C57BL/6 mice

We previously established an IgG Fc receptor IIB (FcγRIIB)‐deficient C57BL/6 (B6)‐congenic mouse strain (KO1), which spontaneously develops rheumatoid arthritis (RA), but not systemic lupus erythematosus (SLE). Here, we show that when Y chromosome‐linked autoimmune acceleration (Yaa) mutation was introduced in KO1 strain (KO1.Yaa), the majority of KO1.Yaa mice did not develop RA, but instead did develop SLE. This phenotype conversion did not depend on autoantibody specificity, since KO1.Yaa mice, compared with KO1, showed a marked increase in serum levels of both lupus‐related and RA‐related autoantibodies. The increase in frequencies of CD69⁺ activated B cells and T cells, and the spontaneous splenic GC formation with T follicular helper cell generation were manifest early in life of KO1.Yaa, but not KO1 and B6.Yaa, mice. Activated CD4⁺ T cells from KO1.Yaa mice showed upregulated production of IL‐21 and IL‐10, compared with the finding in KO1 mice, indicating the possibility that this aberrant cytokine milieu relates to the disease phenotype conversion. Thus, our model is useful to clarify the shared and the disease‐specific mechanisms underlying the clinically distinct systemic autoimmune diseases RA and SLE.